## 5 Discussion
Furthermore, the measurement of green purchasing is not progressing in most municipalities, so there is more room for improvement. The results of our analyses suggest the effectiveness of a GPP. One of the main reasons for its effectiveness is likely that GPP adoption makes it easier to purchase items in bulk. As we discussed in Section 3.1, the relative ease of bulk purchasing is likely one of the main reasons for the successful green purchasing of paper products. GPP adoption changes green purchasing from concerning individual initiatives to concerning organization-wide initiatives. Consequently, the priority of green purchasing becomes higher, and support from senior managers increases [8; 9; 14; 15; 16]. This change facilitates interdepartmental coordination for bulk purchasing or may make interdepartmental coordination unnecessary to purchase in bulk in some cases. There are likely other channels through which GPP adoption affects green purchasing. Nevertheless, we find that GPP adoption is positively associated with the implementation and measurement of green purchasing. Despite the effectiveness of a GPP, only approximately 25% of municipalities have adopted a GPP in Japan. Therefore, the national government should take measures to promote GPP adoption and green purchasing in collaboration with prefectures that have a better understanding of their own municipalities than the national government. As larger municipalities are more likely to adopt a GPP and there is a strong correlation between the advancement of green purchasing and the size of the municipality, such measures would be better targeted primarily at small municipalities. When developing measures for small municipalities, it is important to note that most small municipalities have limited human, financial and other resources for green purchasing. By looking at the descriptive statistics and estimation results, we can identify the following policy implications to promote green purchasing. First, if the accessibility to and identifiability of green products/services is high, then even municipalities with little resources, knowledge and experience for green purchasing may be able to implement green purchasing. Some studies have pointed out the difficulties in the use of environmental criteria for purchasing and procurement [18; 19; 20; 21; 22; 23]. We observe a high percentage of municipalities implementing green purchasing for categories for which there are many coelabeled products (accessibility) or clear environmental criteria for products (identifiability). This observation implies that it is easier for the green purchasing of such categories to spread to small and medium-sized municipalities. Therefore, measures to improve the accessibility to and identifiability of green products may be useful for promoting green purchasing among small and medium-sized municipalities. Second, the promotion of green purchasing has potential for further mitigation of climate change. Notably, green purchasing in public works and air conditioning can result in a large improvement in environmental quality since these categories have relatively large environmental impacts and are likely to have long-term consequences. Moreover, among municipalities with some extent of green purchasing, there is also room for improvement in their measurement of this purchasing. In these municipalities, measuring green purchasing is more effective since the high rate of green purchasing is more meaningful. However, our study fails to address the important issues that were addressed in previous studies. For example, we do not examine how green purchasing performance is affected by some important drivers/barriers to implementing GPP practices, such as knowledge [9; 42; 43; 44; 9; 11; 12; 15; 17; 22; 38; 39; 46], organizational structure and culture [47; 48; 49], government legislation [9; 11; 31; 50; 51; 52; 53; 54], public/citizen pressure [6; 15; 17; 49; 55; 56; 57], NGO influence [15; 31; 58], and supplier issues [6; 42; 45; 59; 60; 61; 62; 63].