## 4 Conclusions  
South Korea is trying to reduce SMD by 33% by 2023 through expanding the collection of it. The implication from this study is all the more interesting since no research that has evaluated people's WTP for reducing SMD is found in the literature. Therefore, this study can be a useful contribution to the literature. In particular, the information about the value people place on the reduction is widely demanded to determine whether the reduction has sufficient public support. For the purpose of providing this information to policymakers, this article empirically looked into people's WTP for the reduction, employing data collected through a survey of 1000 households through person-to-person interviews during July 2019. In addition, the spike model was estimated not only using the entire sample data, including observations with zero WTP, but also only using observations with positive WTP. In this regard, the mean WTP estimate obtained for the sample can be extended over the population. Judging from the comments of the supervisor and interviewers, the survey was implemented without difficulty and successfully enough to collect opinions representative of the population. Overall, people understood the CV questions well and reported the WTP responses in a hypothetical market successfully created with CV. Respondents stated a significant amount of WTP for the reduction. This study can provide three important policy implications. First, people's WTP for reducing SMD was quantitatively assessed. Although 37.9% of interviewees stated zero WTP, the average of the yearly household WTP was calculated to be KRW 5523 (USD 4.92), which is not big compared to the average household's annual income (KRW 58.9 million or USD 52.5 thousand). However, it has statistical significance and can be utilized as a logical basis for the government to continue to push for reduction of SMD. In fact, the various CV empirical studies conducted in South Korea have often encountered too many zero WTP responses [22; 23; 24; 26]. For example, [PERSON] and [PERSON] [22], [PERSON] et al. [23], [PERSON] et al. [24], and [PERSON] and [PERSON] [26] reported that the proportion of zero WTP responses was 56.5%, 46.5%, 61.7%, and 63.6%, respectively. The zero WTP response rate in this study is fairly small compared with the preceding studies. Therefore, it can be judged that the public is giving considerable value to the reduction. Second, according to microeconomics, WTP means the economic benefits that arise from the reduction. The study evaluated the economic benefits that ensue from a 33% reduction in SMD by 2023 through an expansion of its collection and found that the population's total WTP was KRW 110.30 billion (USD 99.75 million). Third, the economic benefits can be compared with the costs caused by the reduction. In this regard, a cost-benefit analysis of the reduction indicated that the reduction is socially beneficial and, therefore, the investment on the reduction can be economically justified. This is because the net present value was larger than zero. Moreover, the benefit/cost ratio was greater than one. Thus, the reduction of SMD should be stably and continuously performed. As addressed above, the CV approach has some limitations due to using a survey of respondents. For example, in a hypothetical market created with CV, payments of a certain amount are not actually made but are made hypothetically. Therefore, it would be useful to conduct a test for the respondents' sincerity that adopts some statistical methods. One method is to include questions which gather ordinal data on a Likert-type scale in the CV questionnaire and then to compute a Cronbach's alpha to test for internal consistency. Unfortunately, this study did not contain the questions in the CV questionnaire. This point needs to be appropriately handled in future CV studies. To the best of the authors' knowledge, there have not been many cases studies that applied CV to reducing marine debris, specifically SMD.