## 3 Methodology
### The Statistical Analysis  
For the statistical analysis of the interviews with scholars and experts [51], besides the in-depth interviews with two professor scholars, there were 13 effective questionnaires of interviews with experts of the circle. The statistical results of the first Delphi questionnaire are as follows: (1) the mode was above 4, (2) the high fitness selection criteria were adopted with the mean \(\geq\)4, and (3) the consistency selection standard deviation was \(\leq\)1. Forty subitems met the above three requirements, which were kept to establish the second Delphi research questionnaire. According to the statistical result of the second Delphi research questionnaire, the high fitness selection criteria were employed with a mean of \(\geq\)4.2, and the consistency selection standard deviation was \(\leq\)0.68. Sixteen subitems meeting the requirements were kept to establish the third Delphi research questionnaire. A statistical analysis of the key subitems of the third questionnaire was conducted via a Kolmogorov-Smirnov one-sample test. The statistical analysis result shows that the expert opinions on each subitem were significant (\(\star\)\(p\) < 0.05). This means that the third questionnaire corrected by Delphi was more reliable and valid than the first one. The mean, mode, and standard deviation of the subitems, the Kolmogorov-Smirnov one-sample test, and progressive significance results are shown in Table 6.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No.** & **Item** & **Mo** & **M** & **SD** &
\begin{tabular}{c} **K–S** \\ **Z-Test** \\ \end{tabular} & **Choice** \\ \hline
**1. Key Factors of Polypropylene Extrusion Sheet Production** & & & & & \\ \hline
1–2 & PP extruder main screw output pressure control & 5 & 4.54 & 0.499 & 1.941 ** & Keep \\ \hline
1–3 & PP extruder polymer temperature control & 4 & 4.46 & 0.499 & 1.941 ** & Keep \\ \hline
1–4 & T-die lips adjustment depends on sheet thickness & 4 & 4.38 & 0.487 & 2.219 ** & Keep \\ \hline
1–5 & Cooling rolls pressing stability & 4 & 4.38 & 0.487 & 2.219 ** & Keep \\ \hline
1–6 & Cooling rolls flatness & 4 & 4.23 & 0.576 & 1.525 ** & Delete \\ \hline
1–7 & Cooling rolls temperature stability & 4 & 4.31 & 0.462 & 2.496 ** & Keep \\ \hline
1–12 & PP sheet width (experts complement) & 4 & 4.07 & 0.615 & 1.248 & Delete \\ \hline \hline \end{tabular}
\end{table}
Table 6: Statistical analysis of the third Delphi questionnaire.  
\begin{table}
\begin{tabular}{l} \hline \hline
4-1 Depends on the clamping force of the thermoformer \\ \hline
4-2 The product and mold maximum layout design arrangement \\ \hline
4-3 The maximum forming height of the thermoformer and product mold design \\ \hline
4-4 The maximum trimming width of the trimmer and product mold design \\ \hline
4-5 The maximum clamping force of the thermoformer and mold forming area design \\ \hline
4-6 Thermoformer motor education ratio \\ \hline
4-7 Trimmer motor reducer and trimming mold weight cutting force \\ \hline
4-8 Trimmer platen opening and trimming mold \\ \hline
4-9 Maximum product depth and trimmer opening \\ \hline
4-10 Thermoforming mold and thermoformer platen center positioning clamping \\ \hline
4-11 Trimming mold and trimmer platen center positioning clamping \\ \hline
4-12 Thermoformer cooling pump flowrate \\ \hline \hline \end{tabular}
\end{table}
Table 5: Key factors of mold and thermoforming line equipment design (12 subitems).