## 3 Results and Discussion
### Statistical Analysis of Group Differences
#### 3.3.3 Mann-Whitney U Test Results  
Pairwise comparisons between groups for each risk factor were performed using the Mann-Whitney U test. All possible group pairwise combinations were as follows:  
1. Group 1 (quadruped robot operator) vs. Group 2 (safety management expert);
2. Group 1 (quadruped robot operator) vs. Group 3 (quadruped robot developer);
3. Group 1 (quadruped robot operator) vs. Group 4 (academic expert);
4. Group 2 (safety management expert) vs. Group 3 (quadruped robot developer);
5. Group 2 (safety management expert) vs. Group 4 (academic expert);
6. Group 3 (quadruped robot developer) vs. Group 4 (academic expert). The Bonferroni correction sets the significance level \(\alpha\) divided by the number of comparisons to \(\alpha^{\prime}\) = 0.05/6 \(\approx\) 0.0083. Table 6 shows the results of the Mann-Whitney U test for the severity of the conflict item. This analysis is a post hoc test performed after the Kruskal-Wallis test, applying a Bonferroni-corrected significance level (\(\alpha\) = 0.0083). According to the results, a statistically significant difference was found between the academic group and the operator group and between the academic group and the safety expert group (\(p\) = 0.007, U = 0 in both cases). A U value of 0 means that the academic group's assessment is extremely different from \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Risk Factor**} & \multirow{2}{*}{**Measure**} & **Group 1** & **Group 2** & **Group 3** & **Group 4** & **Kruskal–Wallis Test Results** \\ \cline{3-8}  & & **Mean Rank** & **Mean Rank** & **Mean Rank** & **Mean Rank** & **\(H\)** & **df** & **\(p\)** \\ \hline Explosion prevention & Severity & 7.8 & 6.1 & 11.13 & 15.2 & 8.161 & 3 & 0.043 \\  & Probability & 10.2 & 6.9 & 7 & 15.3 & 7.518 & 3 & 0.057 \\   performance & RiskScore & 8.5 & 6.7 & 9.13 & 15.5 & 7.072 & 3 & 0.07 \\ \hline  & Severity & 9.9 & 8.7 & 9.25 & 12 & 1.042 & 3 & 0.791 \\  & Probability & 11.3 & 6.4 & 9.88 & 12.4 & 3.452 & 3 & 0.327 \\  & RiskScore & 10.5 & 7.4 & 9.63 & 12.4 & 2.07 & 3 & 0.558 \\ \hline  & Severity & 7.1 & 7.1 & 11.75 & 14.4 & 6.547 & 3 & 0.088 \\  & Probability & 12 & 8.3 & 5.88 & 13 & 4.986 & 3 & 0.173 \\  & RiskScore & 8.8 & 7.7 & 8.25 & 14.9 & 5.334 & 3 & 0.149 \\ \hline  & Severity & 6.5 & 7.9 & 11.25 & 14.6 & 8.293 & 3 & 0.040 \\  & Probability & 14.3 & 4.4 & 9.13 & 12 & 9.153 & 3 & 0.027 \\  & RiskScore & 9.9 & 4.6 & 10.75 & 14.9 & 8.856 & 3 & 0.031 \\ \hline  & Severity & 10.1 & 8.2 & 10.63 & 11.2 & 0.994 & 3 & 0.803 \\  & Probability & 15 & 8.3 & 6 & 9.9 & 6.957 & 3 & 0.073 \\  & RiskScore & 13.2 & 7.6 & 8.13 & 10.7 & 3.141 & 3 & 0.37 \\ \hline  & Severity & 10.4 & 11.6 & 7 & 10.4 & 1.758 & 3 & 0.624 \\  & Probability & 13 & 7.5 & 5.63 & 13 & 6.907 & 3 & 0.075 \\  & RiskScore & 12.2 & 9.3 & 6 & 11.7 & 3.418 & 3 & 0.332 \\ \hline \hline \end{tabular} Note: \(p\) < 0.05 indicates statistically significant results.  
\end{table} 
Table 5: _Cont._the other groups. This suggests that academics perceive the severity of the crash risk significantly differently, possibly more severely than practitioners. The same process was followed for the remaining combinations, and the combinations that showed significant group differences based on the standardized test statistic Z, effect size (r), and \(p\)-value calculated by normalizing the U statistic are summarized in Table 7. In general, we consider a significant difference at the 5% significance level if \(|Z|>1.96\), and the effect sizes (r) and \(p\)-values were calculated using the criteria. Significant differences were observed between groups regarding several risk factors. Statistically significant differences were found between the academic and robot operator groups, as well as between the academic and safety expert groups, in the severity and risk scores for collision and path deviation (\(p\) = 0.007 for all comparisons).