## 2 Methodology and Data  
### Data and Variables  
In this research, whether a public contract is classified as green or not is based on its adoption of green criteria in the contract awarding stage. Green requirements can be applied throughout the whole process of public procurement, i.e., technical specifications (pass/fail entry thresholds), selection criteria, award criteria, and contract performance clauses. To date, the European Commission has developed 19 categories of GPP criteria, each corresponding to one specific group of procurement area, to facilitate member states in applying GPP on the ground [13]. One factor important to GPP concept is life cycle costing; due to this factor, green criteria does not merely focus on the greenness of terminal products, services, or works but extends to checking environmental performance in the whole life cycle of procured objects. It therefore can cover environmental impacts along a typical life cycle of products: raw materials, fabrication, assembly, packaging, transportation, maintenance, disposal. It can also cover the operational qualifications of contractors: management systems, staff capacity, and supply chain management, among other qualifications. We investigated the influential factors of GPP, including the features of the procedures, the purchasers, the suppliers, and the business sectors. The data set we used is the 2018 contract award notice data in \"Tenders Electronic Daily--public procurement notice\" from EU Open Data Portal, \"covering public procurement for the European Economic Area, Switzerland, and the former Yugoslav Republic of Macedonia\". This data shows the most important information in contract award notices like \"who bought what from whom, for how much, and which procedure and award criteria were used\" [14]. We deleted the cancelled contracts and those launched by international organizations (European Union institution or others) from the dataset. The dataset may divide one procurement projects into several observations by using different contractors. We identify observations with IDs of contract award notices; this is one reason why we cannot consider the personal characteristics of individual tenderers. We also dropped 12 contracts out of over 230,000 contracts, whose values were more than or equal to 1E+11 Euros, which at almost 10 percent of a country's GDP is not useful for our analysis. The dependent variable \"green contract\" is a dummy variable for whether the contract is green. We assumed that the contract is green if it mentions at least one of several environmental words (see Table 1) in its award criteria. We collected these vocabularies from 19 EU GPP criteria documents [13]. In addition to the general vocabularies on the environment, like \"environment\", \"sustainable\", etc., there are also words on reduced emissions and toxicity, resource efficiency, ecolabels and criteria, and life cycle cost analysis. The dependent variable \"green contract\" equals one if the contract is green, and equals zero otherwise. Table 2 shows our independent variables, including open procedure (OPE), contract value, product, service, framework agreement, under Government Procurement Agreement (GPA), funded by EU, electrical auction, award method, central purchasing body (CPB), joint procurement, micro/small and medium-sized enterprises (SMEs), number of awarded SMEs, awarded to a group, number of offers, number of awards, as well as dummy variables for ten business sectors. We deem that these potential influential factors correlate with the possibility of a contract being green. Next, these factors are introduced in more detail. The public procurement procedures covered in the dataset include open bids, competitive dialogues, negotiation with or without a call for competition, award without prior publication of a contract notice, and restricted procedure. The value used is value of a contract award notice, in EUR, without value-added tax.