## 2 Materials and Methods
### Final Sample Identification Process  
Based on the two defined research questions, the keywords procurement, tender, bid, award, life cycle assessment, LCA, environmental product declaration, EPD, product environmental footprint, PEF, and carbon footprint were defined for conducting the SLR.  
Figure 1: Overview of Systematic Literature Review (SLR) and snowball approach according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline.  
It must be mentioned that the focus of the article was to analyze the current application of LCA in the procurement process of buildings and identify obstacles to implementation. However, keywords such as environmental product declaration, product environmental footprint, and carbon footprint were also used since LCA can also be closely associated with these terms and was a prerequisite for the generation of EPDs or the calculation of carbon footprints. Moreover, it aimed to enlarge the data pool from the beginning to avoid excluding any articles.  
These keywords were combined in the search string (procurement OR tender OR bid OR award AND \"life cycle assessment\" OR LCA OR \"environmental product declaration\" OR EPD OR \"product environmental footprint\" OR PEF OR \"carbon footprint\") using the Boolean operations \"OR\" and \"AND\". The search for relevant articles was performed in two databases, ScienceDirect and Scopus. In the search, certain constraints were applied to limit the search results to relevant target articles. The first constraint was made based on the search period. The SLR included literature from the years 2000 to 2020. The second constraint was the language of the included literature, which was set to English only. The third constraint was the type of literature, which was set to review articles and research articles. The last constraint concerned the search area of the search string in the two databases. The search string was only applied to title, abstract, or author-specified keywords.  
After applying the search string and the defined constraints in both databases, 569 articles were found. After excluding duplicates, the search comprised 358 articles. After that, the identified articles were further reduced based on the relevance of the title. This process was performed as a double-check, i.e., two persons each performed this step to increase the quality of the exclusion process. After this process step, 241 articles remained, which were further reduced in the next step based on the relevance of the abstract. This process step also took place as a double-check. This exclusion process resulted in 31 articles for the final full paper analysis. Detailed screening of the 31 articles revealed that 13 articles were relevant in answering the research questions and were thus included in the final sample.  
After conducting the SLR, the snowball approach was used as an additional iterative step. In the case of the snowball approach, the reference list was screened from the 31 articles analyzed, and further relevant articles were identified based on references. This first step of the snowball approach resulted in an additional 62 articles, which were reduced to 59 articles after removing duplicates. As with the SLR, the exclusion of articles by the relevance of the title (48 articles left) and abstract (33 articles left) was based on the double-check principle. All the exclusion steps were performed by humans, and no automation tools were used. The detailed full paper analysis of the 33 articles resulted in 6 relevant articles that were included in the final sample. In the end, the final sample for the meta-data analysis consisted of 19 articles.