## 2 Background
### Questionnaire Survey on Green Procurement by Local Governments  
We use a survey conducted by the MOEJ, the \"Questionnaire survey on green procurement by local governments\". This survey collects information on the adoption of GPPs and municipalities' progress in green procurement. The survey began in 2001, and questionnaires are sent to all municipalities every year. The survey has several distinctive and useful features that reveal municipalities' progress in green procurement in Japan.  
First, the survey has very high response rates, approximately 75% on average from 2001 to 2016, with a maximum rate of 96%. In contrast, the literature on green procurement in other countries has suffered from low response rates; for example, [PERSON] and [PERSON] [10] had a response rate of approximately 25% from municipalities and counties in Norway. Similarly, the survey conducted by the Swedish Environmental Protection Agency had a response rate of 58% from municipalities, government agencies, and government companies [35]. Such data sets can cause sample selection bias problems, i.e., the local governments that have a higher interest in green procurement tend to respond. In addition, the Japanese survey data allow us to describe the progress of green procurement by municipalities with lower respondent bias.  
Second, in addition to asking about the adoption of GPP, the survey asks about the extent to which each municipality has implemented green procurement and which products it has procured in such a way. In 2018, the MOEJ expected municipalities to implement green procurement for the following 21 categories: paper products, stationery, office furniture, imaging equipment (e.g., printers, scanners, projectors), electronic devices (e.g., laptop or desktop computers), office equipment, mobile phones, home appliances, AC units, water heaters, lighting equipment (e.g., light emitting diodes), cars, fire extinguishers, uniforms, bedclothes, work gloves, other fiber products (e.g., tents, flags), other equipment (e.g., water-saving devices, solar power cells), emergency supplies (e.g., emergency food/water, portable batteries), public works (i.e., contracts with private firms, in terms of infrastructures), and other public services (e.g., dining hall-related goods in government offices, cleaning-related goods in government offices).  
In asking about the extent of the green procurement of these products and services, the questionnaire requires respondents to answer by choosing one of the following seven categories: \"Almost 100%\", \"More than 80%\", \"80% to 40%\", \"Less than 40%\", \"Do not know the extent\", \"Have the criteria but have not purchased any yet\", and \"No purchasing\". The first four categories imply that the respondents have implemented green procurement and calculated the ratio of green products and services to total purchase amount, while \"Do not know the extent\" implies that the respondent does not know the ratio. The remaining two items imply that the respondent has not yet begun purchasing greener products. However, \"Have the criteria but have not purchased any yet\" also indicates at least that the respondent has some criteria for green procurement (though not a GPP itself), such as a list of greener products or criteria for identifying which product is appropriate for green procurement.  
In this paper, we focus on the survey conducted in 2016 because it is the latest version available to researchers and the most comprehensive version in terms of the targeted items. Moreover, we can ignore the change in the number of municipalities and their sizes over years, which were caused by several mergers following the enactment of the Special Merger Law in 1995. The number of municipalities was 3234 in 1995; however, this figure had decreased to 1724 by 2018. The largest change in the number of municipalities occurred from 2003 to 2006. During that period, the number of municipalities diminished from 3196 (the beginning of April 2003) to 1827 (the end of March 2006).