# Understanding Safety Performance of Prefabricated Construction Based on Complex Network Theory
## 3 Methodology
### Data Collection
#### 3.1.2 Obtain the Relationships between Safety Risks  
Upon confirming the safety risks affecting prefabricated building projects, a self-completion postal and online questionnaire-based survey was developed to quantitatively assess the interactions among the acquired risks, including the number of ties, for the network theory-based analysis of the next step. The questionnaire consists of four parts. The first part is the introduction; the second part aims to investigate the basic information of participants, including institution/company, working position, and related working experience; the third part seeks to judge the interaction among safety risks of prefabricated building projects, and acknowledgment is in the last part. As the core of the questionnaire, the third part was designed in the form of risk structure matrix (RSM), which was expanded from design structure matrix (DSM) introduced by [PERSON] [81]. DSM enables the relations and dependencies among workflow activities in the system to be represented and analyzed, while RSM facilitates identifying interactions among the risks associated with these activities [82]. RSM is a binary and square matrix, where the row position is regarded as the initiator of the relationship, and the column position as the receiver of the relationship. If \(R_{i}\) is believed to exert an influence on \(R_{j}\), that is, the occurrence of \(R_{i}\) may lead to the occurrence of \(R_{j}\) (regardless of the probability), the number 1 is filled in the corresponding space; otherwise, 0 is filled. Figure 3 shows an example of the RSM representation of a risk network. With the exclusion of the strength of links, the questionnaire only requires respondents to judge and score possible relationships of risks in the matrix questionnaire box. Therefore, the measure applied in the research can alleviate the confusion and divergence in link establishment and evaluation, and effectively reduce the recognition work in the questionnaire, which contributes to improving the quality of the questionnaire recovery. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Risk ID** & **Risk Name** & **Design** & **Subordinate Stage** & & \\ \hline R33 & Adverse weather condition & & & \(\bullet\) & \(\bullet\) & [26,47,74,75] \\  & Utilization of heavier and & & & & \(\bullet\) & [27,76,77] \\ R34 & large prefabricated & & & & \(\bullet\) & [27,76,77] \\  & components & & & & \\  & High exposure to & & & & \(\bullet\) & [31,78,79] \\ R35 & hazardous material & & & & \(\bullet\) & [34,52,71] \\ R36 & Poor performance of the & & & & \(\bullet\) & [39,80] \\  & motion planning & & & & \(\bullet\) & [39,80] \\ R37 & Thoughtless site & & & & \(\bullet\) & [39,80] \\  & construction scheme & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
Figure 3: (**a**) Example of relationships among risks, (**b**) Example of RSM. To cover as many different stakeholders to take part in the questionnaire survey as possible, this study adopted two sampling strategies comprising simple random sampling strategy and snowball sampling strategy. The snowball sampling strategy involves designating a specific participant among stakeholders, who then recommends and invites other stakeholder groups and representatives to participate in the questionnaire. Then the referral process is repeated until the survey covers all important and representative stakeholder groups. Easy-to-contact and cooperative representatives from China's leading prefabricated construction companies were selected to start the recommendation process. The invited representatives were then requested to investigate their colleagues in the company and appoint other stakeholder groups and representatives directly involved in the construction of the prefabricated building projects. Furthermore, simple random sampling was used as a supplement to the snowball sampling strategy to attract more professionals to participate in the survey.