## 2 Materials and Methods  
### Construction of Quality Risk Evaluation Indicator System for Assembled Building  
#### 2.1.1 Identification of Quality Risk Factors for Assembled Building  
To accurately assess the quality risk of assembled building, it is necessary to identify the potential influencing factors and to establish a perfect quality risk evaluation index system based on these factors. How to correctly select the risk evaluation indicators is particularly important as too many indicators will lead to the complexity of the assessment process, increase the difficulty of decision-making, and influence the effectiveness of risk management, while too few indicators may lead to the inability to comprehensively quantify the risk so that the evaluation results lack of depth and accuracy, and then they cannot effectively identify and respond to the key issues arising in the actual project. Therefore, in order to ensure the rationality and accuracy of the evaluation results, this paper adopts the following five-step process to identify the potential risk factors affecting the quality of assembled buildings in strict accordance with the principles of science, systematicity, objectivity, and operability in order to construct the index system, see Figure 1. These indicators cover the five key stages of the entire process of prefabricated construction and can effectively assess the probability, consequences, and concealment of quality risks. In addition, the indicator system is not fixed and can be dynamically adjusted according to industry development, emerging technologies, and specific project characteristics to ensure its scientific nature, comprehensiveness, and practicality. (1) Literature search and preliminary screening  
Through CNKI, Web of Science, Wanfang Library, and other platforms, we searched for the keywords \"quality of assembled buildings\", \"quality risk\", and other keywords to identify the risk evaluation indexes, set the search time to 2015-2024, found a total of 264 related pieces of literature, sieved out the reports, conferences, etc., to get 213 effective pieces of literature, from which the common risk factors were extracted to form the initial index library. (2)  
Accident case studies  
We combined these pieces of literature with the quality accident cases in assembly building projects in the past 5 years, analyzed the causes of the accidents using the \"4M1E\" theory (personnel, materials, machinery, methods, environment), and identified representative risk factors. Classification and optimization of indicators  
Based on the division of the whole project process of assembly building into five main stages (decision-making and design, bidding and procurement, production and transportation, on-site assembly and construction, and operation and maintenance) and considering them as guideline layers [14; 15], the indicators of the above initial screening were categorized. Applying the Work Breakdown Structure and Risk Breakdown Structure [16] (WBS-RBS) in the graphical method, indicators with high repetition or low relevance are eliminated and optimized to form a scientific and reasonable indicator library. Expert consultation (Delphi method)  
Ten experts in the field of assembly building with different working years and positions were invited to assess the importance, scientific nature, and operability of the indicators through multiple rounds of consultation. Experts helped to finalize the 20 secondary indicators through a scoring system and feedback. Construction of the final indicator system  
On the basis of the expert assessment, an evaluation index system for quality risk of the whole process of assembled buildings is established, which includes three levels: target level, criterion level, and index level, of which the criterion level includes five first-level indexes, and the index level includes 20 second-level indexes, as shown in Table 1.  
Figure 1: Risk indicator screening flowchart.