## 5 Conclusions and Future Work
For instance, (1) the trust and risk attitudes of the DMs could be combined to reduce the impact of evaluation data from low-trust DMs on the decision-making process, as well as to create a metric that can be adopted to ascertain the consistency of the evaluation data. (2) The virtualization software or 3D printing could be used to validate product design solutions, thus increasing the availability of data for assessing the feasibility of PSS conceptual solutions during the early design phase. Conceptualization, L.J. and D.F. ; Writing--original draft, D.F. ; Investigation, X.F. ; Writing--review and editing, L.J. ; Funding acquisition, S.J. and X.F. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China [under grant numbers 52105282 and U1610112], the Project funded by China Postdoctoral Science Foundation [2021M702893], and the Zhejiang Provincial Natural Science Foundation of China [under grant number LY20E050020]. The authors acknowledge the anonymous Editor and reviewers for valuable comments and suggestions. The authors declare no conflict of interest. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{5}{c}{**(a) Scheme Value Assessment of Evaluation Criteria on the PSS Design**} \\ \hline \multirow{2}{*}{**Evaluation Criteria**} & \multicolumn{4}{c}{**Evaluation Value Assigned by Four DMs**} \\ \cline{2-5}  & **DM1** & **DM2** & **DM3** & **DM4** \\ \hline P1 & 4 & 3 & 3 & 4 \\ P2 & 6 & 4 & 4 & 3 \\ P3 & 7 & 8 & 4 & 4 \\ P4 & 5 & 5 & 4 & 3 \\ P5 & 6 & 4 & 4 & 5 \\ P6 & 4 & 6 & 3 & 5 \\ P7 & 4 & 6 & 4 & 6 \\ P8 & 5 & 4 & 6 & 3 \\ P9 & 5 & 6 & 6 & 8 \\ P10 & 4 & 4 & 4 & 6 \\ \hline \multicolumn{5}{c}{**(b) Scheme Value Assessment of Evaluation Criteria on the Economy**} \\ \hline \multirow{2}{*}{**Evaluation Criteria**} & \multicolumn{4}{c}{**Evaluation Value Assigned by Four DMs**} \\ \cline{2-5}  & **DM1** & **DM2** & **DM3** & **DM4** \\ \hline E1 (t) & 2.25 & 2.75 & 1.5 & 2.25 \\ E2 (km/h) & 16 & 20 & 16 & 13 \\ E3 (mm) & 3000 & 4000 & 4000 & 4000 \\ E4 (kw) & 6 & 8 & 6 & 4 \\ E5 (yuan) & 14,400 & 12,000 & 12,000 & 14,400 \\ E6 & 6 & 6 & 7 & 5 \\ E7 & 4 & 6 & 7 & 5 \\ E8 (t) & 4.5 & 5 & 3 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Initial evaluation matrix of the electric forklift PSS concept (taking the CS2 as an example). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{5}{c}{**(a) Scheme Value Assessment of Evaluation Criteria on the PSS Design**} \\ \hline \hline \multirow{2}{*}{**Evaluation Criteria**} & \multicolumn{3}{c}{**Evaluation Value Assigned by Four DMs**} \\ \cline{2-5}  & **DM1** & **DM2** & **DM3** & **DM4** \\ \hline P1 & 5 & 8 & 8 & 3 \\ P2 & 4 & 3 & 3 & 2 \\ P3 & 7 & 4 & 3 & 2 \\ P4 & 5 & 7 & 3 & 5 \\ P5 & 6 & 3 & 4 & 4 \\ P6 & 5 & 6 & 6 & 6 \\ P7 & 6 & 2 & 3 & 5 \\ P8 & 5 & 4 & 6 & 6 \\ P9 & 5 & 7 & 8 & 7 \\ P10 & 5 & 3 & 3 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Initial evaluation matrix of the electric forklift PSS concept (taking the CS4 as an example). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{5}{c}{**Evaluation Criteria**} & \multicolumn{3}{c}{**Evaluation Value Assigned by Four DMs**} \\ \cline{2-5}  & **DM1** & **DM2** & **DM3** & **DM4** \\ \hline P1 & 7 & 4 & 6 & 6 \\ P2 & 7 & 6 & 6 & 6 \\ P3 & 6 & 5 & 6 & 5 \\ P4 & 6 & 5 & 6 & 7 \\ P5 & 5 & 4 & 4 & 5 \\ P6 & 7 & 6 & 3 & 6 \\ P7 & 7 & 6 & 5 & 6 \\ P8 & 7 & 8 & 6 & 5 \\ P9 & 7 & 7 & 4 & 7 \\ P10 & 7 & 6 & 6 & 7 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Initial evaluation matrix of the electric forklift PSS concept (taking the CS3 as an example).