Post-Handover Quality Management Index of Electric Housing Work

. Since housing electrical work is essential in the aspect of electricity use and electrical accidents, it is necessary to properly design, construct, and manage it to avoid quality problems. However, disputes are intensifying in Korea due to numerous quality problems after the house is handed over to the owner. Although related standards have been established and some studies have been conducted, there is a lack of discussion on housing electrical work because the housing quality problem is varied. In this study, the cases of quality problems that occurred in housing electrical works were investigated, while 52 quality control indices were presented and classifed according to detailed work category, object, and problematic occurrences. In addition, the number of cases of quality problems for each quality management index and the repair cost ratio were used as a scale to understand the status of quality management. Finally, 11 quality indices were suggested as candidates of important indices which needed to be controlled to focus on the housing electrical work by comparing the above 52 indices. Te comparison was made on which one was best suited to the Pareto principle, a quality management strategy, among the candidates for the critical index and the indices suggested by relevant standards and previous studies. Te comparison results showed that the candidates of the essential indices suggested in this study conformed to the Pareto principle, while other indices hardly conformed to it. Terefore, if the quality control strategy of choice and concentration for housing electrical works is used, focusing on these vital index candidates can efectively assist in handling the occurrence of quality problems.


Introduction
Te quality of housing is an important index that can express producer competitiveness. If a house of excellent quality meets the consumer's expectations, it ultimately leads to high satisfaction [1]. Customer satisfaction brings a good reputation for the producer and is often settled as a brand representing the producer's image [2]. Tis good reputation generates a positive efect, such as repurchasing-house built by that producer or recommending to others [3,4]. Te consumer also makes a reasonable purchase to procure excellent quality houses as much as possible. Some consumers sometimes search for better quality housing even if they already possess houses [5]. In addition, there is an argument that housing quality is closely related to socioeconomic status [6]. As discussed above, the supply and consumption of excellent quality housing become beneft for producers and consumers.
Terefore, housing producers seek a good evaluation through various gestures after the house's handover to the consumer. Te postconstruction quality is evaluated using a criterion, the Customer Satisfaction Survey. Te National Housing Building Council (NHBC) and Home Builders Federation (HBF) are housing company organizations in the UK that investigate and publish the satisfaction of house purchasers. According to the survey conducted in 2022 [7], 91% of the house consumers in the UK responded positively that they would recommend those housing companies to others. Such satisfaction of housing consumers increased by 7% during the last fve years. However, the Homeowners Alliance (HOA) survey, an organization of homeowners in the UK, showed somewhat diferent results. According to the survey resulted in 2019 by the HOA [8], 87% of the housing consumers want security, which is not a warranty for defect repair, to be directly deposited. Tis implies that defect repair is not satisfactory from the viewpoint of the house consumer. Terefore, trust in housing quality should be improved.
In Korea, there are cases in which diferent standards for housing quality are created and evaluated. Te Korea Productivity Center under the Ministry of Trade, Industry and Energy, which is a national institution in Korea, evaluates various aspects of housing quality using a scale called the National Customer Satisfaction Index (NCSI). Among the indices for the housing sector, the housing brand values for the top 8 companies are evaluated. Te average index from 2011 till 2021 steadily dropped till 2015 and assumed an increasing trend till 2021 [9]. Since disputes over quality can be regarded as a standard for housing quality, the Defect Review and Dispute Mediation Committee under the Ministry of Land, Infrastructure, and Transport of Korea plays a role in mediating disputes regarding housing defects. Te number of disputes received by this Committee by 2021 amounted to 37,116, which is increasing yearly [10]. Considering this, the national customer satisfaction index for housing brand value is rising, but the housing quality perceived by consumers is still insufcient.
Construction, including housing, is executed through a combination of civil, architectural, mechanical, electrical, telecommunication, and landscape works [11,12]. Terefore, efective management is needed through cooperation and synchronization between sectors [11,12]. Although eforts are made to optimize design and construction among construction participants, it is challenging to secure satisfactory quality in all aspects [13,14]. For example, cracks frequently occur due to drying shrinkage in the concrete structure [15]. In the wooden structure, cracking occurs due to changes in moisture content [16]. If appropriate preservative treatment is not given, fungus attacks or damage from insects such as termites occur [17,18]. In some cases, the joining method of the pipe is not adequate, or the pipe is installed with a material that is unsuitable for use, which leads to leakage earlier than the expected service life cycle of the pipe [19,20]. As enumerated above, various problems that deteriorate quality may occur throughout the housing.
In the housing's electrical work, various problems also occur. Although the service life of various facilities or electrical cables used in electrical work is not precisely known, these cannot be used forever [21]. Moreover, electrical load or usage difers depending on the household members and their lifestyles [22]. In addition, the problem can occur due to excessive electricity use in a specifc season [23]. Terefore, a variety of electrical problems may occur. Te short circuit is the most frequently occurring problem in electrical work [24]. Electrical short circuits occur if the electrical wire covering is damaged or defective parts are used [25]. When a short circuit occurs, the circuit breaker operates whenever an electrical device is used [26], making electricity unavailable in all or parts of the house. In this case, the lights are not on, making it challenging to work at night [27], and all foods in the refrigerator may be spoiled [28].
However, the most crucial problem with electric housing work is that it causes fres. Electrical problems account for a large proportion of fre accidents. In the United States in 2019 alone, 50.2% of home fres were caused by cooking and 7.5% were due to electricity-related defects [29]. In the case of the UK, as of 2021, the most signifcant number of fres were caused by cooking appliances, followed by electrical distribution and electrical appliances [30]. In Korea, as per the statistics in 2020, 27.6% of all fres occurred in housing. Moreover, among the causes of fre, electricity accounted for 24.1% of the total and was the second most crucial cause [31].
In addition, equipment and parts of electrical work contain heavy metals harmful to the human body. Mercury is a luminant in electric lamps and batteries for a small portion [32]. Lead is used to monitor glass and soldering, which does not melt the substrate at a relatively low temperature among welding methods [33]. Bromine is used as a fame retardant to suppress fre [34]. Tese heavy metals are gradually reduced due to environmental regulations or institutionally banned [35]. However, even a tiny portion of heavy metals can be fatal to the human body. Terefore, environmental and health problems may occur due to waste generated while repairing defects in electric work.
In order to improve the quality problem of the aforesaid housing electrical work, it is necessary to frst identify which type of problem occurs. Te research trends on the identifcation and solution of quality problems in housing electrical work are as follows. Conti and Orcioni analyzed the defect rate in components such as thin-flm transistor boards and control boards [36]. Shipp et al. identifed three common causes by analyzing the defect cause of transformer failure. In addition, an alternative that could alleviate the primary circuit breaker switching transient due to voltage surge was proposed [37]. Considering the environmental load or energy efciency, solid-state lighting (SSL) has recently drawn the limelight over conventional lighting such as incandescent and fuorescent lamps. However, according to Lall et al., SSL still has quality problems. Remarkably, they pointed out the problems of exposure to heat and excessive moisture due to long-term use, such as landscape lighting installed outside a housing complex. Specifcally, they listed the defect types such as carbonization of the encapsulant material, delamination, and lens cracking [38]. During the construction of a house, there is a possibility that moisture may remain in the conduit that is embedded in the concrete.
Furthermore, moisture may exist in the conduit due to dew condensation as temperature changes. In this regard, the study of Hwang et al. pointed out that the Halogen-Free Flame Retardant Poly Olefn Insulation Wire (HFIX wire) in the conduit absorbed moisture, causing the insulation to break down and trip [39]. In the case of a high-rise house, an elevator is essential for residents to move. Terefore, various problems may occur in high-rise houses because the elevator is continuously operated. In the study conducted by Ha, elevator failure data for 17 years were collected and analyzed by time of failure, building use, elevator type, and failure parts. It was found that the most failures occurred in summer season, in houses among building uses, in passenger elevators among elevator types, and in semiconductors in 2 Advances in Civil Engineering control panels among components [40]. As seen above, studies on major facilities and devices used in electrical works are being actively conducted. However, although they have studied in-depth the equipment that caused defects, they did not go into the overall quality problems that occurred in the housing electrical work. In Korea, as disputes over housing quality have rapidly increased after handing over a house to the owner, there are standards established to smoothly resolve disputes. Tese are the construction appraisal practice [41] proposed by the court and the defect judgment standard [42] enacted by the Ministry of Land, Infrastructure and Transport, which oversees the construction sector. However, although the construction appraisal practice deals with overall appraisal, it does not include the housing electrical quality problem in detail. In the case of defect judgment standards too, only some of the quality problems of electrical works are stipulated. Furthermore, there have been very few previous studies conducted on housing electrical works, which will be discussed in detail in Chapter 2. Most of the previous studies conducted on the quality problem of housing electrical works have been limited as part of the equipment [43][44][45][46][47][48][49][50], and there are limited studies that have been conducted focusing on the housing electrical work [51,52]. Terefore, it is necessary to specify the quality problems that occur in the housing electrical work and to have standards such as the quality management index that can represent whole fgure.
In addition, in order to practically use the quality management index, it is necessary to be able to set management goals, and a comparison scale for setting the goals is also required. However, the previous study, which will be described later, failed to suggest a management goal for improving housing quality problems. If there are too many quality problems and it is practically difcult to handle all of them, it is reasonable to select important ones among them and improve them intensively. For that purpose, a comparison scale should be presented as a selection method. However, only some cases proposed the number of defects [43][44][45][46]51], number of cases [52], repair cost [44], etc. as comparison scale in the previous studies. Moreover, there was no case of suggesting a methodology for setting management goals using comparison scales. Terefore, a methodology including the setting of management goals and comparison scale for improving the quality of housing electrical works should be proposed.
In order to achieve the above agenda, in this study, the quality management index that describes the quality problems occurred in the housing electrical work after handover the house to the owner in detail is proposed to help the overall quality problems to be identifed quickly. In addition, it is necessary to propose a method of comparing quality management indices as a comparison scale for each quality management index by adopting number of dispute cases and the defect repair cost ratio, and then combining these. Trough this process, it would be possible to understand the status of the housing electrical work, and it can derive a method for selecting an important index. Finally, by comparing the important indices proposed in this study with those presented in each standard and literature, a quality management strategy that best meets the status of housing electrical construction is proposed.

Quality Management Index.
For the quality problems in the housing electrical work, it is possible to establish a quality management index that can identify the overall problem by specifying the problem by identifying types and amount of problem. However, in most cases, quality problems are unfavorable to housing producers, and it is not easy to obtain relevant data. Even in major previous studies on housing quality issues, it is often found that the source of the research data is unclear or not specifed at all, and in some cases, the relevant institutions refuse to provide the data.
If we look at how the quality management index is stipulated in the standards for dealing with quality issues, the Society for Construction Lawsuit in Seoul Central District Court in Korea has established a guideline called Construction Appraisal Practice (CAP) that includes housing quality issues [41]. Since the construction appraisal practice provided guidelines for litigation, it was expected that the litigation data would be the basis. However, in the construction appraisal practice, types, depth or level, and amount of collected data were not described at all. In construction appraisal practice, the quality management index for electrical work consists of three items: (1) no fexible conduit installed inside the bathroom ceiling, (2) defective built-in appliances, and (3) defective lighting fxtures. As another standard, the Ministry of Land, Infrastructure and Transport of Korea established the Defect Dispute Mediation Committee to deal mainly with housing quality disputes. In this committee, defect dispute mediation is being carried out using what is called A Judge Standard, investigated the method, and estimated costing of Defect in dwelling House (JSDH) [42]. Tere is a diference between the above two standards: the construction appraisal practice is mainly used in cases where disputes are resolved through litigation, and the defect judgment standards are used for resolving disputes through mediation. In the defect judgment standard, the quality management index for housing electrical work is defned as 6 categories of (1) non-installation of fexible conduit inside the bathroom ceiling, (2) poor lighting, (3) defect in lighting grounding, (4) installation of lighting equipment diferent from the drawings, (5) detachment of lighting, and (6) unconnected lighting.
However, as will be described later in Sections 4.3 and 4.4, the quality management index of construction appraisal practice and defect judgment standard seems to have limitations, although these are standards based on dispute cases, that it is extremely limited compared to reality. In addition, no standard discloses the basis or method of selecting the quality management index for the housing electrical works. Tey focus only on investigating defects using the quality management index, and do not suggest directions or methods for improving quality management. From a generality point of view, the quality management index intensively manages the cases where defects occur frequently Advances in Civil Engineering or the cost of repairing damages is high [53]. Terefore, it is difcult to consider these standards themselves as goals for quality improvement.
Next, we will look at what data were used to derive quality management index while the major previous studies worked on the quality management index. Similar studies have been conducted on concrete exterior house wall defects [54], defects in housing mechanical equipment [55,56], and landscaping defects in apartment complexes [57]. Te research trends for housing electrical work are as follows. Georgious et al. requested data from the Housing Guarantee Fund Ltd. (HGF), an Australian housing quality assurance agency, and the Royal Australian Institute of Architects (RAIA), which conducts a quality survey to investigate the quality problems of Australian housing. However, HGF refused to provide data on the grounds of commercial secrecy. Terefore, Georgious et al. stated that they utilized the housing inspection report for the housing quality problems of Archicenfre, under the RAIA Institute of Architecture as data [43]. Taking their statement on the research, the data used by Georgious et al. appear to have a high-level expertise and objectivity. Meanwhile, Georgious et al. classifed defects in 1,772 houses in Australia by dividing them into works inside of housing complexes, exterior work, and interior work. Tey classifed 12 types of detailed defects. However, the electrical work was not separately classifed, and the mechanical work and the electrical work were grouped and classifed as facility work. In addition, they disclosed that 9 types, including broken/deteriorated, were identifed among 12 types of defects in the housing facility work. However, among them, it is impossible to fnd out how many defects occurred in the electrical work, and the specifc object or phenomenon was not described.
Te study by Kim et al. was based on the data from 1,769 housing units in Korea where residents requested defect repair [51]. However, since residents are not housing experts, it is difcult to regard that the data presented by them accurately stipulates the quality problem. Even in litigation, problems of use or disputes between residents are sometimes claimed as defects, so in order to utilize the data presented by residents, it is necessary to go through a review by a related expert. However, in the paper by Kim et al., it was not stated that research was conducted based on the data arranged through such process. Meanwhile, Kim et al. divided housing electrical works into fve groups: electricity, telecommunication, frefghting, TV public watching, and other works. However, it is not reasonable to classify them as electrical works from the fact that the Korean Housing Act classifes communications, frefghting, and TV public watching as separate works in addition to electrical work, and orders for these works are raised separately. On the other hand, Kim et al. divided the defect types of electrical works into defects in design stage and defects in construction stage. In the design stage, four types of defects were presented, such as diferent cable specifcations and lightning protection equipment specifcations, and eight types of defects such as outlet defects and switch failures were presented as defects in the construction stage.
Lee's study targeted 16,631 housing units in Korea and indicated that he analyzed data from a defect-related institution, but he did not disclose the source [44]. Lee divided housing works into architecture, civil engineering, machinery, electricity, communication, and frefghting, and suggested the type of defect for each work type. Among them, electrical work was divided into seven categories, such as poor lighting and poor location. Lee suggested lighting and elevators as specifc subjects for the quality problem, but other things are not clearly specifed. Meanwhile, Lee revealed that he put all other items as other works other than the quality management index he proposed, and the repair cost of these other works accounted for 43.6% of the total. Terefore, even if it is judged based on the data presented by Lee, Lee's quality management index for electrical work may not be a representative.
Yu has researched 2,297 households in Korea, revealing that, like the previous study by Kim et al., the study was performed based on the data requested by residents to repair defects [45]. In addition to electrical work, Yu also includes architectural and mechanical felds. Yu classifed the quality management index of electrical works into 9 types: general defects, lighting failures, lighting cover breakages, and switch failures. However, there was no specifcation on what the general defect defned by Yu means. Moreover, the repair cost of general defects accounted for 55% of the electrical work, and it seems that Yu's classifcation of the quality management index for electrical works is inappropriate same as in Lee's study.
Forcada et al. classifed 2,179 housing complexes in Spain into defects that occurred within the housing complex, defects that occurred outside the building, and defects occurred inside the building [46]. However, according to Forcada et al., it was suggested that these quality problems were difcult to represent as they were constructed by one contractor. Terefore, the data of Forcada et al. appear to be based on the data presented by the housing producers. Meanwhile, Forcada et al. classifed electrical works as facilities along with mechanical works. In addition, the quality management index of electrical works defned the target as electrical fxtures and lighting devices (electrical light and power), and the study does not include information on problematic phenomena.
Choi conducted study on 48 complexes in which lawsuits regarding quality issues were fled against housing in Korea [47]. Te litigation in Korea is based on the investigation on the quality issues by the court-appointed experts such as architects and technicians. Terefore, just like the study of Georgious et al., the data used by Choi seems reasonable in terms of professionalism and objectivity. Meanwhile, Choi studied the warranty period and repair cost for quality problems. Tis was for the entire house and included electrical works, but it did not suggest a specifc quality management index for electrical works.
Love et al. targeted 217 Australian building, infrastructure, and rail projects, based on data provided by producers [48]. Tey compared each project entity, size of defect repair cost, detailed construction work, and cause of defects. Te project entity was divided into owner, designer, general contractor, and sub-contractor, and detailed facilities were classifed into 22 categories. Among them, electricity-related work was divided into two categories: electrical work and lighting work.
Chisholm analyzed the efects of quality problems of house on health and safety of residents by interviewing 83 homeowners in New Zealand [49]. Chisholm's study is meaningful that it was a study conducted from the viewpoint of residents, mainly in terms of health and safety of the residents. However, because the evaluation of residents lacked technical expertise, the quality management index based on that survey has limitations. In fact, among the quality control indices suggested by Chisholm, for electrical works, it was limited to electric power supplies, switches, and home appliances, and quality problems were simply classifed by location. In addition, there was no specifc classifcation by phenomenon.
Park et al. derived a quality management index in their study for housing electrical works based on lawsuits fled in Korea [52]. Te quality management index for electrical works suggested by Park et al. was subdivided into 29 types, and these are listed in Table1, which will be described later. Park et al. only targeted housing electrical works and presented the largest quality control indices among the previous studies. Tis study has further subdivided the quality management index by Park et al. for housing electrical works.
Te study by Chohan et al. was related to the method of investigation of the quality problem of housing in Malaysia [50]. However, they did not disclose the specifc study subjects. Tey classifed 10 building defects according to the location of the house and further subdivided them into 55 house defects. Among them, electrical works were classifed as service defects, and the quality management index defnes only one, electrical fxtures and switches.
Summarizing the results of the review of the previous studies above, it is necessary to secure objective data to approach the quality problem of housing electrical works, but such cases seem to be rare. Te research based on the data investigated by experts such as Georgious et al. and Choi looks more objective. Also, as most of the studies dealt with housing quality issues, the quality management index for electrical works was limited. Terefore, in order to rationally derive the quality management index for housing electrical works, objective data should be secured, and the contents related to electrical work should be abundant. Tis study intended to present a quality management index using data from litigation on housing quality issues in Korea.

Comparative Measures and Application.
If the quality management index of the housing electrical works has been selected, it is necessary to identify the quality management level of the housing electrical work to use the quality management index, set a management goal that matches it, and prepare an achievement strategy. As mentioned above, only the quality management index itself is to be used in the quality dispute-related standards, and the quality management measures that developed the quality management index was not presented. Terefore, in this section, the quality management measures suggested in the previous studies will be reviewed.
Georgious et al. used the defect rate as a scale to express the quality management index, but they did not include the number of cases or repair costs [43]. Also, they emphasized the sharing of knowledge and information among housingrelated institutions, associations, universities, and cooperatives, but failed to suggest specifc goals or methods for quality improvement.
Kim et al. performed a study based on the repair request data of residents. However, even if all of them were considered quality problems since they did not use the number of other cases or repair costs, no goals or alternatives combining these indices were presented [51]. Nonetheless, they suggested the cause and improvement measures of quality index for each electrical work. Kim et al. presented only the status of problem occurrence, which has limitations based on applications from non-professional residents. Moreover, they did not include the process of separately analyzing the cause of the problem and deriving improvement measures in their research, nor did they cite the diagnosis by a separate expert to identify the cause or suggest countermeasures.
Lee's study used the number of occurrences of quality problems and the repair cost as scale for the quality management index [44]. In addition, the excess and shortage of repair costs were compared for each space where the problem occurred and the detailed construction work. Lee has proposed the supplemented quality control checklist of the housing producers as a plan for cause of defect occurrence and improvement. However, as with Kim et al. above, the study did not include any intermediate steps that were connected to the results of Lee's analysis and subsequent causes of defects or improvement measures. Te study by Yu [45] was not much diferent from that of Kim et al. or Lee. Te study by Forcada et al. did not focus on comparison or evaluation between quality management indices, but compared defects identifed by the builder at the time of housing construction with those identifed by residents after handover [46]. Accordingly, it was shown that there is a diference in quality standards in view of the diferent eye level of the builder and the occupant. However, Forcada et al. did not set specifc quality management goals, and the mentioned alternatives were just ordinary ones and had no direct relationship with the analysis content.
Choi's study compared repair cost and home warrant deposit as indices for quality management [47]. As a specifc quality management goal, it was suggested as a research question whether the repair cost would exceed the home warranty deposit, and in the result of the case analysis, the repair cost was below the defect deposit standard. However, it was for the whole housing quality problem, and there was no particular about the electrical work.
Te study by Love et al. compared the diference in repair cost according to the type of project and suggested that the repair cost due to quality problems was about 6 times higher than the initial construction cost [48]. It was also suggested that the diference was mostly due to ordering or design problems. However, it was for the construction industry in a Advances in Civil Engineering whole, and a detailed comparison of electrical works was not included.
Chisholm's study was a comparison scale for the housing quality management index, and unlike other studies, it was based on the satisfaction of homeowners [49]. However, his study also did not suggest specifc goals, nor did it suggest alternatives specifc to electrical work.
Te study by Park et al. used the number of defective cases as a comparison scale for the quality management index of housing electrical works [52]. Trough the study, quality management indices could be compared with each other, and relatively important indices could be distinguished. However, since this study was based only on the number of cases, there was a limitation that it was impossible to determine the magnitude of damage each quality management index caused because a scale such as repair cost was not used.
In summary, the study which suggest a specifc comparison scale for using the quality management index was rare. In some studies, the number of defects, the number of cases, the cost of repairs, and questionnaires or interviews were presented as comparison scale, but previous studies interpreted them as they were and could only use them fragmentarily. So, there was a limitation that those could not propose a new evaluation index by appropriately combining comparison scales, nor even suggest a quality management goal accordingly. Terefore, it is necessary to present a standard that can compare the quality management index of housing electrical works, and to present a new evaluation index or management goal that combines them.

Framework.
Tis study consists of fve parts according to the framework of Figure 1, and accordingly research was carried out sequentially. Specifc targets, data collection and analysis methods for this purpose are described in the next section.
(1) Data collection: Collects information such as items and types of defects in housing electrical works listed in related regulations, previous studies, and housing defect dispute cases. (2) (2) Preparation of Quality Management Index (QMI): Preparing QMI by classifying defects according to detailed work, object, and phenomenon from the data collected in (1). Te example shown in Figure 1 is described in A1, which is the QMI preparation process for the non-installation of fexible conduit in the ceiling. In A1, detailed work is  Table 2, which will be discussed later.
(3) Calculation of Issued case quantities (ICQ) and Repair cost ratio to total cost (RC ratio): If defects are confrmed in the case data for each QMI in (2), they are counted as ICQ, and the repair cost is counted as RC and RC ratio. Te example shown in Figure 1 (2) is indicated. In (3), the ICQ and RC ratios aggregated for each QMI are set for each axis of the two-dimensional plane, and the QMI position is marked on the corresponding plane. Te RC ratios for the QMI groups in each quadrant are aggregated. Figure 1 shows the process of classifying the quadrant where A1 is located. In this study, the important item index was constructed focusing on items with frequent defects and high maintenance cost (items belonging to F-H quadrant) and items with infrequent defects but high maintenance cost (items belonging to S-H quadrant). Tis study specifed multifamily housing among various types of housing. For multifamily housing, the subject of this study, the law stipulates that these multifamily houses must comply with the basic design standards set by the government [59]. Since multifamily houses have parallel quality standards, there is a high probability that defects will occur in similar types and targets. Terefore, a statistically signifcant result can be expected from comparing defects in apartment houses. In addition, multi-family houses are relatively easy to obtain data because of the large number of houses being built.

Case Collection.
Tis section describes the frst stage of the framework in Figure 1 above. As discussed in the previous Chapter 2, some of the defnitions for the object and phenomena of the quality problems in the related regulations and previous studies on the housing electrical works were quoted. Te detail can be checked from 4.3, 4.4, and 4.5, which will be described later.
Meanwhile, the quality dispute case data was analyzed again based on the data used by Park and Seo [52]. Te data were from lawsuits fled against housing quality in Korea. Tis document investigated quality issues after the home was handed over to the owner. Te court appoints a separate construction feld expert to investigate and report housing quality issues. Te expert who performs this task is called an appraiser. Te appraiser checks the quality problem, decides the repair method and scope by work type and location, and calculates the repair cost. Tese results are included in the appraisal report and submitted to the court [60]. Te court makes a judgment by adopting some of the contents of the appraisal report and rejecting others. In general, items related to electrical work and repair costs are specifed in the litigation judgment, but in some cases, they are not separately stated [61]. Terefore, this study extracted necessary data from judgments and appraisal reports of housing quality dispute lawsuits.

Standardization of Quality Management Index.
Tis section describes the second stage of the framework in Figure 1 above. Te Housing Quality Management Index (QMI) used in the lawsuit is named by the party who raised the issue. However, homeowners lack professionalism, making terminology and expression methods vary signifcantly from case to case; therefore, the items listed in the collected data were not standardized. Tis study extracted items related to electrical work from case data, and similar items were mutually adjusted and integrated. According to the work type, objects, and phenomenon, these standardized items are called the quality control indices, and the subject includes electrical facilities and equipment. For example, a wire and cable, pipe, lighting, outlet, circuit breaker, etc., represent electrical facilities or equipment. A phenomenon is a specifc problem considering defects, including malfunction, breakage, non-installation, etc. Each QMI detail can be confrmed in Table 2, which will be described later.

Measure of Quality Management Index.
Tis section describes the third stage of the framework in Figure 1 above. Tis study proposed a management system with the prime index at the center to utilize the quality control index for electric works. Te number of disputed cases (ICQ: Issued Case Quantity) and the repair cost ratio (RC ratio: Repair Cost Ratio to Total Cost) were used to evaluate the prime indices.
Te number of dispute cases was counted as in equation (1), with 1 being the case where a defect occurred in each index among all cases and 0 being no defect occurrence. Terefore, since the number of study cases was 100, the number of disputed cases ranged from 0 to 100. If the number of dispute cases for a specifc index was large, it could be regarded that defects occurred frequently.
ICQ � C 1 + C 2 + C 3 + · · · C n . (1) Te repair cost ratio was calculated in equation (2) as a percentage obtained by dividing the repair cost of each index by the sum of the repair costs for electrical work. Accordingly, the repair cost ratio ranged from a minimum of 0% to Advances in Civil Engineering 9 a maximum of 100%. If the repair cost ratio of a specifc index was high, it caused much damage.
RC ratio � Repair cost of the item Total repair cost × 100(%). (2) On the other hand, since the case data in this study were obtained from the lawsuit, the timing of the determination of defects and repair costs was diferent. Since the repair cost should consider the diference over time, it is necessary to organize it under a consistent standard. As of the current time when this study is conducted, the repair costs for all cases had already been determined in the past. Terefore, the repair cost of each case was converted using the Future Value (FV) method as of the end of December 2021 at the time of the study. As in equation (3), the future value could be calculated by assuming the discount rate (Interest: I) and the elapsed period (Year: n) between the present value (PV) and the base point as in equation (3). For the discount rate, the three-year interest rate of 1.8% on treasury bonds (KTB) announced by the Central Bank of Korea was applied [62].
3.6. Prime Index Candidate Draw. Tis section describes the fourth stage of the framework in Figure 1 above. In this study, selecting the prime index among the quality control indices of housing electrical works was applied using the method proposed by Park and Seo's study [53] that applied the Pareto principle. As shown in Figure 2 below. Each QMI is expressed as a scatter plot according to the number of dispute cases and the ratio of repair costs. Moreover, it is divided into S-L, F-L, S-H, and F-H based on the arithmetic mean value of the number of dispute cases and the ratio of repair costs. Afterward, the number of dispute cases and the level of the remuneration ratio of the index belonging to each quadrant were checked. In the case of QMI belonging to the F-H area, it can be important because the number of dispute cases is signifcant on average, and at the same time, if a problem co-occurs, a high defect repair cost is required. On the other hand, QMI belonging to the S-L area is insignifcant because the number of dispute cases is small and the defect repair cost is also low. Terefore, between the contrasting QMI on the F-H area and the QMI on the S-L area, the one that meets the critical index will be the QMI on the F-H area.
Although QMI belonging to the S-H area is not a frequent problem, its repair costs are high if it does occur. On the other hand, although QMI belonging to the F-L area is a frequently occurring problem, it requires a minor repair cost. Unlike F-H and S-L, where importance can be clearly distinguished, it is difcult to assert which one is more important in these two cases. Terefore, the one with the higher total defect repair cost ratio of the QMI in each quadrant may be given priority, or, in some cases, both may be adopted as an essential index.
If the number of these critical indices was around 20% of the total index, and the sum of the repair cost ratios accounted for more than 80% of the total repair cost ratios, it was judged that this met the typical Pareto law [63,64]. Conversely, it was checked whether the trend was consistent with the long-tail law, which was contrary to it [65,66]. If the quality management system for electric housing works follows the trend of Pareto's law, it is adequate to perform quality control based on important indices for electric housing works. Conversely, if the distribution according to the extended tail theory is shown, it is necessary to devise measures to improve quality control throughout the electric housing work.

Comparison on Index.
Lastly, this section describes the ffth stage of the framework in Figure 1 above. Te method of verifying whether the vital index derived in this study is appropriate by comparing the electric work quality control index is as follows. Based on Index A, which was the entire case, the construction appraisal practice (CAP) was compared with Index B, and the defect determination standard (JSDH) was used as Index C. Index B and Index C were used as standards for handling housing quality disputes in Korea. It was expected that by comparing them, the level of standards could be understood, and suggestions for systematic supplementation could be proposed. In addition, Park and Seo [20], which had the most subdivided index among the preceding studies, was named Index D and added as a comparison subject. Index A, the three indices to be compared, and the candidates for the prime index of this study were named and compared as Index E. Te ratio of the number of indices to Index A (index ratio to Index A) and the composition of the repair cost ratio were examined to see which one best ftted Pareto's law. Moreover, the result was selected as a prime index representing the quality management system of the electric housing works.  Figure 3, the study case was 100 apartment housing complexes in South Korea, with 991 dwelling buildings and 81,431 households. Tey have been used for 1 to 10 years after the house was completed. Geographically, they were often located in Seoul, Incheon, and Gyeonggi-do, Korea's capital areas. In these cases, 439 items were identifed for disputes regarding electrical work. Te total repair cost confrmed by a lawsuit judgment was 1.47 billion KRW, and when the exchange rate as of the end of December 2021 was applied, it amounted to 1.26 million USD (1 USD � 1,179 KRW).

Standardization: Index A.
For Index A, collected cases were reviewed and defned the quality dispute items occurred in the houses as QMI according to detailed construction work, object, and phenomenon. Te results were classifed into 52, as shown in Table 2. Figure 4 shows the QMI of Index A according to the type of detailed work as per the Housing Act in Korea. As a representative, Electric Pipe and Wiring Work were the most common with 18 cases (A1∼A18). Lighting Equipment Work followed with 12 cases (A19∼A30). On the other hand, there was no corresponding QMI in Lightning Conductor Work and Power Equipment Work. In addition, the six subindices (A47-A52), which are difcult to classify as detailed works stipulated by the Korean Housing Act, were classifed as other works. Tese are sensors attached to equipment, devices, etc. or those classifed as design defects. Figure 5 shows the QMI of Index A by object. Lighting was the most common with 12 (A19∼A30), and Wire and pipe was classifed into 10 (A1∼A10). Figure 6 presents QMI of Index A by phenomena. Malfunction was the largest with 17 followed by Non-installation with 14. Figure 7 shows the aggregation of the number of dispute cases (ICQ) for QMI in Index A. Lighting malfunction (A19) occurred in 42 cases out of 100 cases and occurred most frequently. As for the number of dispute cases in Index A, the arithmetic mean was 6.12, with 15 sub-indices exceeding the average and 37 sub-indices below the average, indicating that there were many sub-indices below the average. Figure 8 shows the ratio of repair ratio to QMI of Index A. Te elevator main device malfunction (A44) took the most repair cost. It was found that the arithmetic mean of the repair cost ratio of each QMI was 1.92%. Tere were 10 QMIs above the average and 42 sub-indices below the average. Terefore, there were more QMIs with less than average repair cost ratio. Table 3 shows Index B, which is the electrical work QMI specifed in the construction appraisal practice [42]. It consists of a case of no installation of a fexible conduit inside the bathroom ceiling (B1), a case of defective built-in home appliance (B2), and defective lighting equipment (B3). Figure 9 shows a Pareto graph depicting the repair cost ratio percentage for each Index B subindex among the collected cases. B0 was the sum of all items not specifed in Index B. Among the codes of Index B, the repair costs were in the sequence of 16.07% for B3, 8.55% for B1, and 0% for B2. Te sum of the repair cost ratios for the subindices in Index B was 24.14%. On the other hand, B0, not included in Index B, reached 75.86%. Table 4 shows Index C, which is the housing electrical work QMI specifed in the defect judgment standard [43]. It consisted of six cases of non-installation of a fexible conduit inside the bathroom ceiling (C1), poor lighting (C2), poor lighting grounding (C3), installation with a lighting fxture diferent from the design drawing (C4), lighting missing (C5), and unconnected lighting (C6). Figure 10 is a Pareto graph showing the repair cost ratio for each subindex of Index C among research cases. C0 is the sum of all other defects not specifed in Index C. In Index C, C2 had the highest value at 16.07%, C4 at 8.99%, C1 at 8.55%, and so on. Te repair cost ratio for the subindices in Index C was 34.09%. On the other hand, C0 not included in Index C was 65.91%. It was confrmed that the repair cost ratio of the indices belonging to the defect determination criteria was higher than that of the construction appraisal practice. Table 1 shows Index D, which is the housing electrical work QMI defned by Park and Seo [53]. Index D consists of a total of 29 QMIs, as shown in Table 1. Figure 11 shows the Pareto graph with the repair cost ratio of Index D. D0 is the sum of all defects not specifed in Index D and accounted for 31.34%. Among Index D, D11 was the highest at 16.02%, followed by D23 at 12.3% and D13 at 8.99%. Te sum of all repair cost ratios of Index D is 68.66%. 4.6. Index E. As mentioned in Section 3.6, Index E was selected as an essential index candidate by comparing the number of dispute cases (ICQ), and the repair cost ratio (RC ratio) among the QMIs of Index A. Figure 12 below shows each QMI as a scatter plot with the number of dispute cases on the X-axis and the repair cost ratio on the Y-axis. In addition, the comparison results by dividing into each quadrant based on the average of the number of dispute cases (ICQ) of 6.12 and the average of the RC ratio of 1.92% are as follows.

Index D.
First, 34 numbers of QMIs, such as A8, A9, and A10, marked with gray circles, belong to the S-L area located at the lower left of Figure 12. Te sum of the repair costs for each QMI in the S-L area is about 6.29%, which is lower than in other areas. Also, in the S-L area, the number of dispute cases (ICQ) and the repair cost ratio (RC ratio) are lower than the average. Terefore, it does not occur often, and even if it does, the damage seems insignifcant.
Second, seven QMIs, A2, A4, and A5, marked with yellow circles, belong to the F-L area located at the lower right of Figure 12. Te sum of the repair costs for each QMI Advances in Civil Engineering in the F-L area is about 5.55% of the total. Tis fgure is lower than the S-L area, but since the number of QMIs in the F-L area is signifcantly smaller than that in the S-L area, it is difcult to ascertain that the weightage of repair costs is low. Meanwhile, although the F-L area occurs frequently, the damage seems small.
Tird, A7, A18, and A44, marked with a red triangle, belong to the S-H area located at the upper left of Figure 12. Te sum of the QMI repair costs in the S-H area is about 28.3%. Although the S-H area has only three QMIs, the repair cost is higher than that of the S-L and F-L combined. Although the frequency of occurrence of these defects is minor, the repair costs are high if they occur, so they potentially cause much damage.
Fourth, eight QMIs, such as A1, A3, and A14, marked with blue rectangles, belong to the F-H area located at the upper right in Figure 12. When all the QMI repair costs in the F-H area are summed up, they account for 59.86% of the total. Tese seem to occur frequently and take high repair costs.
Combining the results of comparing the number of dispute cases and the repair cost ratio for the QMI of Index A above, the S-L area or F-L area, which has a relatively low frequency of quality problems and low repair costs, has many QMIs but takes low repair costs. Te total repair cost of QMIs belonging to these two areas is only 11.84%, but the number of QMIs is 41, which is 78.8% of the total. Terefore, this does not conform to the Pareto composition that intends to select a vital quality management index. As for QMIs in the F-H area, where quality problems frequently occur and repair costs are also high, and in the S-H area, where the defect occurrence frequency is low but high, repair costs are 11 or 21.2% of the total.
It is considered reasonable to regard it as a valuable index candidate. Terefore, this study selected 11 Figure 13 shows the subindex and repair cost ratio of each index. Since the Index A included all detailed indices of electric housing work derived through case analysis, the detailed index and repair cost ratios of Index A were 100%, respectively.
In Index B, as shown in Figure 13, the subindex ratio was 5.77%, and the repair cost ratio was 24.14%. Index B had the lowest subindex ratio among the indices to be compared and the lowest repair cost ratio. Te Pareto Principle stated that 80% of all outcomes came from 20% of all factors. However, since the ratio of the detailed indices of Index B was 5.77%, it was within 20% of the total factors according to the Pareto rule. However, since the repair cost ratio was only 24.14%, it was far below the result of the Pareto law of 80%.
In Index C, the subindex ratio was 11.54%, and the repair cost ratio was 34.09%, as shown in Figure 13. Te subindex ratio of Index C was about twice that of Index B, but it was within 20% of the Pareto law factor. Moreover, Index C had a 10% higher repair cost than Index B. However, it seemed to fall short of the 80% result of the Pareto Principle.
In Index D, as shown in Figure 13, the subindex ratio was 55.77%, and the repair cost ratio was 68.66%. Since the repair cost ratio of Index D was 68.66%, it was about 2-3 times higher than Index B or Index C, which was noticeably high. However, it did not conform to the result of the Pareto principle of 80%. In addition, the subindex ratio of Index D far exceeded the 20% factor of the Pareto principle. Terefore, selecting all the QMIs in Index D as essential indices for the quality management system for housing electrical works is difcult.
In Index E, it can be seen from Figure 13 that the detailed index ratio was 21.15%, and the repair cost ratio was 88.16%. Te subindex ratio of Index E was 21.15%, which was 20% of the factor of Pareto's law. Since Index E's repair cost ratio was 88.16%, it was more than 80%, resulting from Pareto's law. Terefore, Index E could be regarded as a system that conformed to Pareto's law, as the subindex ratio was 20% of      Repair cost ratio to total cost (%)   the total and the repair cost ratio was more than 80% of the total. Considering these points, Index E was considered an important index representing the quality system of electric housing works.

Discussion
As discussed earlier, this study proposed a quality management index (QMI) that could identify the general quality problems in the housing electrical work after the house was handed over to the owner. In addition, using two comparison scales of the quality management index, the number of cases of quality problems (ICQ) and the repair cost ratio (RC ratio), a method for setting management goals for quality problem improvement was proposed. Based on these research results, what improvements could be drawn compared to the past and what they suggest will be discussed in this chapter.

Quality Management Index and Prime Index of Housing
Electrical Work. Housing electricity is vital in terms of functionality and safety for residents' lives. However, most previous studies focused on the overall housing quality problem, and housing electrical work was rarely discussed. Nonetheless, according to the results of the previous case studies, various quality problems occurred in the posthandover stage of housing electrical work, and the amount of quality problems generated and the cost to repair them were also signifcant. Trough this study, along with the opinions of some previous studies, it was possible to confrm that the quality problem of housing electrical works exists and is also important.
Regarding the quality problems in housing electrical works, related standards and previous studies also suggested some types. However, most of them focused on felds other than electrical work, so they could not describe it in detail. On the other hand, Kim   focused on the quality problem of housing electrical works and presented detailed defect types. Tis study went one step further than these studies on the quality problems of housing electrical works. A quality management index that was specifcally and systematically classifed according to detailed work, object, and type was presented.
In the previous study, the number of defects, number of cases, and repair cost were used as indices to determine how signifcant the quality problem of housing electrical works was. However, the previous studies interpreted these indices as they were and could not establish new standards by applying them or suggesting specifc ways to use them. On the other hand, this study adopted the number of cases and repair cost among the indices suggested in the previous studies and combined them to understand the overall quality of the housing electrical work. In addition, a method for comparing the quality management index was presented. Te comparison results showed that a critical index representing the quality problem of the housing electrical works could be developed to the suggested level.
On the other hand, if the index is to function as an essential index of the housing electrical work, it should be able to represent the overall quality problem sufciently. However, the previous studies did not specifcally reveal how much their research results could represent the quality problem of housing electrical works. Accordingly, based on the case data collected in this study, a comparison was made to select a better index among the quality management indices of the previous studies and major indices of this study that can represent the quality problem of housing electrical works. As a result of comparison based on the total repair cost, the previous study accounted for 5.77% of the total repair cost at the lowest and 55.77% in the highest case. Tis does not conform, however, to the Pareto principle, a representative quality control method, and does not conform to the long tail rule, which is the opposite case. In addition, no specifc quality management method was suggested in the previous studies, and even if the analysis results were followed, it seems complicated to relate them to other quality management methods. On the other hand, in the important index suggested in this study, 80% of the result was caused by a 20% level of the cause, confrming that it was following the typical Pareto principle. Terefore, it is considered that this study's important index not only represents the quality problem of housing electrical works, but also applies the quality control strategy related to the Pareto principle.

Improvement Plan to Quality Management.
As discussed above, since the important indices presented in this study tended to conform to the Pareto principle, it can be considered to apply the accompanying choice and concentration strategy to the quality management of housing electrical works. Terefore, a method to utilize the important index, as shown in Figure 14 below, is proposed, and it can be precisely divided into the two following stages (tracks).  In the frst stage (track 1), as shown in the upper part of Figure 14, the quality management index and important index, the quality management suggestions of this study, were adopted as such and set and managed as a quality management goal for each company or unit site. For the quality management of each company, it is desirable to establish an optimized quality management measure by identifying the company's status according to the procedure outlined in the framework of this study. However, if the company size is small or there are not many projects to be carried out, it is difcult for an inexperienced manager to establish a basis for setting quality management goals. Terefore, this study's quality management index and important quality index can be a suitable strategy for start-ups or small businesses in the housing business. Since the important index of this study was selected based on the analysis of numerous cases, it can be regarded as fully refecting the business conditions, so the important index, the result of this study, can be set as an explicit management goal. It is desirable to repeat the process until a suitable number of cases are accumulated and then switch to the second stage below.
Te second stage (track 2) explains where each company establishes and operates its quality management plan according to the framework presented in this research method, as shown at the bottom of Figure 14. If a company carries out enough projects and there are many managers with various experiences, a quality management plan can be established based on the results of collecting their case data and analyzing them using the method of this study. Te head ofce can draw up a quality management index at the company-wide level, derive an essential index, and then apply it to each site to serve as a driving force to strengthen quality management. In addition, each site can optimize quality management by modifying the management goal and comparing the critical index sufered by the head ofce with the site's conditions. Te quality control results of these sites are sent back to the head ofce so that the entire company's    Unit : (%) Figure 13: Pareto comparison on all indexes. 18 Advances in Civil Engineering quality management level can be checked and compared between sites. In addition, lacking points and sites with poor performance are identifed to seek focused improvement at the company-wide level. By repeating this stage, data can be continuously collected, and lessons from successes and failures can be accumulated to adjust the quality management measures.

Conclusions
In order to improve the quality of housing electrical works in the post-handover stage, a standard that can identify the overall problem must be prepared. In addition, a methodology that includes a quantitative scale for setting and comparing management goals is required. For this purpose, this study collected housing dispute case data and classifed housing electrical work quality problems as a quality management index. Furthermore, as a comparison scale for each quality management index, a method of comparing the quality management indices was proposed using the number of dispute cases and the ratio of defect repair costs. In addition, a strategy was proposed to focus quality management capabilities on important indices that conform to the Pareto principle based on the repair cost. Although the construction entity must have delivered the house to the owner after judging that the house is complete and there are no problems, the analysis results of this study show that various quality problems occur in the post-handover stage. Terefore, construction entities should use the results of this study as an opportunity to make further eforts to prevent the occurrence of quality problems in the future. In addition, since the quality management index or important index of this study is an alternative based on problems that occur in housing electrical work, it is helpful in practical terms because it can be applied to on-site quality management as it is. On the other hand, this study also has the following limitations. Depending on the design level and type of a house, the details of electrical work may vary, and the usage environment is diferent, so in some cases, important quality problems that no one expected may arise. In addition, as social issues such as energy saving and carbon reduction are raised, various regulations are being added during house construction. In the case of housing electrical work, the introduction of energy-saving lighting devices is becoming mandatory. Even solid-state lighting, a representative energy-saving lighting device, has a shorter life span than expected, and various problems are reported from the beginning. Terefore, there is a limit to responding to all quality problems only with the quality management index or important index of the housing electrical work for currently constructed houses. In the future, it is necessary to exchange information on new quality issues and discuss technical supplementation methods according to the business environment and technological changes.

Data Availability
Te data used to support the fndings of this study are available from the corresponding author upon request.

Conflicts of Interest
Te authors declare that there is no conficts of interest regarding the publication of this paper.