## 3 Empirical Studies
### Experimental Procedure  
The sequences of disposal of e-wastes into the collection box are not predictable, so the disposal order is regarded as an uncontrollable variable. In addition, the number of activated sensors and the signal of the unclosed lid are observable, while the actual accumulated volume of disposals in the collection box is not observable and is regarded as the latent variable. Therefore, it is required to analyze the sensor information, such as the total number of and the incremental number of activated signals. To conduct this investigation, first, the stratified sampling method is adopted for selecting the test units according to the ratio of S&M e-wastes disposed of annually. Table 1 shows the annual disposal quantities of S&M e-wastes from the annual report of the KERC. Due to practical limitations, only 32 test units are selected and actually applied in this study. Table 2 illustrates each volume of test unit. Next, to reflect the actual situation of disposal by considering the uncontrollable variables, such as the disposed product type and the disposal sequence, completely randomized disposal orders of S&M e-wastes were generated [23; 24]. The generated number of groups composed of the randomized disposal order of S&M e-wastes was 20, and each group was tested with 5 trials repeatedly. Each trial with different sequences of disposals was terminated right before the accumulated volume of disposals reached over 70% of the collection box because each disposal has its own discrete and distinguished volume. The event is defined as two cases. The first case is the situation in which the number of \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Year** & **14** & **15** & **16** & **17** & **Total** & **Ratio (\%)** \\ \hline Computer (including Video player and Cassette) & 7,448,392.1 & 6,116,630.3 & 8,673,632.9 & 6,956,572.5 & 29,105,128 & 32.2 \\ Electric fan (including Humidifier) & 2,826,085.4 & 6,567,948.4 & 8,016,177.5 & 5,619,750.4 & 23,029,962 & 25.2 \\ Printer & 2,020,621.4 & 2,396,688.1 & 2,785,188.9 & 4,224,168.4 & 9,628,666.7 & 10.4 \\ Copy machine & 1,249,504.6 & 2,401,901.8 & 3,641,162.3 & 2,146,052.7 & 9,429,657.3 & 10.2 \\ Vacuum cleaner & 1,413,977.7 & 1,147,674.6 & 1,929,575.5 & 1,138,867.6 & 1,514,060.8 & 6.7 \\ Electric rice cooker & 317,669.73 & 1,188,752.6 & 1,286,596.5 & 726,585.7 & 3,519,604.6 & 3.8 \\ Audio & 656,131.1 & 7,333,135.5 & 5,978,965.4 & 2,278,492.9 & 2,563,143.6 & 2.8 \\ Microwave & 500,852.5 & 4,099,603.6 & 666,786.36 & 26,604.69 & 1,884,936.6 & 2.1 \\ Dish dryer & 170,489.68 & 225,619.66 & 33,334.38 & 391,020.6 & 1,140,464.3 & 1.2 \\ Electric bidet & 171,841.21 & 245,677.76 & 323,774.6 & 337,295.91 & 1,024,053.81 & 1.1 \\ Electric oven & 180,893.92 & 229,145.88 & 275,871.51 & 2,664.7 & 892,587.57 & 1.0 \\ Air purifier & 132,998.57 & 156,827.96 & 27,499.27 & 249,754.62 & 721,082.22 & 0.9 \\ Mobile phone & 384,208.84 & 234,663.6 & 7,000,52.2 & 11,223,402.4 & 70,156.36 & 0.8 \\ Electric purifier & 145,651.64 & 143,979 & 187,227.42 & 61,235.74 & 583,093.8 & 0.6 \\ Facsimile & 90,205.83 & 657,084.8 & 98,826.9 & 4,321,442.4 & 298,029.24 & 0.3 \\ Blender & 69,112,111 & 801,071.74 & 8,956,44 & 5,019.2 & 286,114.94 & 0.3 \\ Food waste disposals & 33,038.46 & 31,648.4 & 39,899.03 & 29,863.55 & 134,412.24 & 0.2 \\ Water softener & 16,410.71 & 11,950.12 & 24,350.48 & 50,858.56 & 103,097.17 & 0.1 \\ Electric iron & 16,760.4 & 24,144.48 & 25,871.84 & 28,710.96 & 95,487.68 & 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Annual disposed quantities of small and medium (S&M) e-wastes.