## 2 Materials and Methods
### Method: CV  
The CV method has various advantages and disadvantages. Three advantages are as follows. First, unlike revealed preference approaches, such as the hedonic price technique and the travel cost technique, CV is a stated preference technique and can be used to estimate the economic value that explicitly includes non-use value. Second, from an economic point of view, the CV technique can theoretically provide an accurate estimate of the economic value or benefits from the supply of a certain good, while the revealed preference techniques have room for underestimation or overestimation. Third, since the validity and reliability of the CV approach is proven to some extent in the literature [22; 23; 24; 25; 26], the CV approach has been a widely applied one. The CV method also has three disadvantages. First, the application of CV is more costly than that of other economic techniques because a survey of many respondents is essentially needed. For researchers facing budget constraints, the application of CV may be restrictive. Second, a valuation through CV based on the data collected using the questionnaire can be subject to various biases, as it can be influenced by the content of the questionnaire, the attitude of the interviewer, and the operation of the survey method. Third, since CV techniques are based on stated responses gathered from people instead of human behavior, people are less likely to believe in the value obtained by using CV. The DC question method has several merits and demerits. There are two typical merits to the DC method. First, it is quite familiar to respondents. Even if a person has not experienced a referendum, the type of question is similar to deciding whether to buy a good on the market. Therefore, people can answer DC questions without much difficulty. Second, it is incentive compatible for people to respond. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{} & \multicolumn{4}{c}{**Lower Bid is Suggested First (\%) b**} & \multicolumn{4}{c}{**Higher Bid is Suggested First (\%) b**} & \multicolumn{4}{c}{**Number of Observations**} \\ \hline
**Bid Amount a** & **“yes-yes”** & **“yes-no”** & **“no-yes”** & **“no-no”** & **“yes”** & **“no-yes”** & **“no-no-yes”** & **“no-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** & **“No-no-no”** \\  
People buy a certain good if their utility from the purchase and consumption of it is greater than or equal to the price of the good; they do not otherwise buy the good. If a person's WTP is greater than the presented bid, she/he will answer \"yes\" and otherwise \"no.\" There is no reason to take a strategic behavior when a person is faced with the DC question. The DC method has two demerits. First, the use of the DC question results in discrete interval data rather than continuous point data. This makes an econometric analysis of the CV data less statistically efficient than other value elicitation methods such as open-ended questions. Thus, the use of the DC method requires the collection of a large number of observations and demands a large survey cost. Second, a pretest survey is required to determine a list of bid amounts to be presented to the respondents, resulting in costs associated with the pretest survey and longer application period than other methods. Reducing SMD is a typical nonmarket good. A nonmarket good means that it cannot be traded in the usual market. A good traded in the market is easily valued, but a nonmarket good does not have a market and its value is not well observed [27]. Therefore, for the purpose of assessing the economic benefits ensuing from the reduction, it is necessary to create a hypothetical market for the reduction and hypothetically trade the reduction in the market. A CV method is a typical economic method that can be done in this way, and it has been widely utilized in the literature [28; 29; 30; 31; 32; 33; 34].