## 3 Results and Discussion
### Discussion of the Results  
This study investigated people's WTP for reducing SMD in South Korea by 33% by 2023 by means of expanding SMD collection. It is possible to compare three sample characteristics with three population characteristics given in Statistics Korea [47]. First, the sample proportion of female persons can be compared with the population proportion of female persons. The first (50.0%) is not different from the second (49.9%). Second, three areas with a large number of households can be investigated. The sample proportions of Gyeonggi, Seoul, and Busan respondents were 23.9%, 20.1%, and 7.2%, while the population proportions of Gyeonggi, Seoul, and Busan respondents were 23.7%, 19.4%, and 7.0%, making no significant difference. Third, the average monthly income of households can be examined. The sample value was KRW 4.86 million (USD 4136) and the population value was KRW 4.92 million (USD 4187), almost the same. The authors also think that the population could be reasonably represented by the sample because sampling was entrusted to a specialized survey institute. Therefore, extending the results for the previously presented sample to the population would not be a problem. One of the most important purposes of the applied CV study was to expand the location value of WTP obtained from the sample to the population. In this regard, we should have determined whether to use the location values for the sample. Usually, mean, median, and mode are used for location value. The median WTP obtained in this study was zero and the mean WTP was estimated to be positive. The mode WTP could not be computed because we used DC WTP question. It was necessary to determine which, of mean or median, to use. Median is known to be all the more robust than mean because mean is vulnerable to outliers but median is not. Median can be useful for identifying the central tendency of the sample, but it is not used for expanding a sample value to a population value because it can cause underestimation to overestimation in the expansion. Therefore, the mean WTP has been almost always employed in the literature to estimate population value using sample value. As explained earlier, we conducted stratified random sampling using 16 strata. The sample size allocated to each stratum was decided based on the Census implemented by Statistics Korea in 2015. The sample size of each stratum was, thus, consistent with the population. In this study, the total value was calculated by multiplying the mean WTP by the number of households in the population instead of using a mean formula applied for stratified sampling. The average of the household's yearly WTP for the reduction was computed as KRW 5523 (USD 4.92). This sample value can be extended to the population. The population's total WTP was derived as the multiplication of the relevant number of households by the average WTP. Since the \begin{table}
\begin{tabular}{l c c} \hline \hline  & **Variables** & **Estimates** & **\(t\)-Values** \\ \hline Constant & \(-1.1772\) & \(-1.80\) * \\ Bid amount 1  & \(-0.1803\) & \(-21.29\) ** \\ Education & 0.1252 & 3.90 ** \\ Income & 0.1221 & 4.32 ** \\ Head & \(-0.1881\) & \(-1.54\) \\ Age & \(-0.0122\) & \(-1.66\) * \\ Spike & 0.3769 & 24.65 ** \\ Yearly household mean willingness to pay & KRW 5412 (USD 4.82) \\ \(t\)-value & 21.01 ** \\
95\% CI 3  & KRW 4946 to 5965 (USD 4.41 to 5.31) \\
95\% CI 4  & KRW 4778 to 6123 (USD 4.26 to 5.45) \\ Sample size & 1000 \\ Log-likelihood & \(-1297.06\) \\ Wald statistic (\(p\)-value) 5  & 607.79 (0.000) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Estimation results of the model containing the variables described in Table 3.  
CV survey was conducted throughout the country, the relevant population became the entire country. There were 19,971,359 households when the survey was implemented [47]. The yearly population value would be KRW 110.30 billion (USD 99.75 million). Comparison of this value with the costs involved in the reduction is an interesting task.