*4.2. Identification of Key Factors*

Based on the former status analysis, the effects of different sectoral solid waste production coefficients and sectoral direct consumption coefficients on USWS performance can be quantified. The designed factors, and corresponding experimental scenarios, are presented in Table A2. Figure 4 presents half-normal plots of the standardized effects. The further a factor lies away from the red line, the corresponding effect is more obvious. The significant factors that affected the SPI were AM\_a, PM\_a, AM\_e and PM\_e. The most important factor causing solid waste pollution in Fujian Province was AM\_a, which contributed 64.71% in 2012 and 51.14% in 2017, followed by PM\_a accounting for 22.01% and 37.04%. SPI was sensitive to the changes in sectoral direct consumption coefficients of AM and PM. These results implied that unit GDP solid waste production of AM and PM were higher than in other sectors. The contributions of AM\_a decreased and PM\_a increased in 2017, indicating that the Fujian Province gradually focused on the economic development of PM.

Figure 5 shows the effect plots of significant factors, which described the single and joint effects of the imperative factors on SPI. In Figure 5(a1,b1), results indicate that PM\_a, AM\_a, ELE\_a and OTH\_a had negative effects on SPIm, while other factors had positive effects on SPI. For example, in 2012, the average value of SPI was 0.632 under L level of PM\_a and 0.533 under H level of PM\_a. To reduce the SPI of USWS, the increment of factors that had negative effects, and the decrement of factors that had positive effects, might be helpful. In terms of joint effects presented in Figure 5(a2,b2), the most significant interactions between two sectors were CON\_e\*OTH\_e in 2012 (contributed 1.53%) and TRA\_e\*OTH\_e in 2017 (contributed 2.53%). The two crossed lines denote that the effect of another factor changes when one factor is at different levels. These demonstrated that control of the economic products of social service sectors (e.g., public infrastructure

management sub-sector, culture, sports and entertainment sub-sector) can help reduce the SPI, even if the amounts of solid waste production of CON and TRA increased.

**Figure 5.** Effect plots of significant factors. (**a1**) main effect in 2012; (**a2**) joint effect in 2012; (**b1**) main effect in 2017; (**b2**) joint effect in 2017.
