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Experiences from using snowballing and database searches in systematic literature studies

Background: Systematic literature studies are commonly used in software engineering. There are two main ways of conducting the searches for these type of studies; they are snowballing and database searches. In snowballing, the reference list (backward snowballing - BSB) and citations (forward snowballing - FSB) of relevant papers are reviewed to identify new papers whereas in a database search, different databases are searched using predefined search strings to identify new papers. Objective: Snowballing has not been in use as extensively as database search. Hence it is important to evaluate its efficiency and reliability when being used as a search strategy in literature studies. Moreover, it is important to compare it to database searches. Method: In this paper, we applied snowballing in a literature study, and reflected on the outcome. We also compared database search with backward and forward snowballing. Database search and snowballing were conducted independently by different researchers. The searches of our literature study were compared with respect to the efficiency and reliability of the findings. Results: Out of the total number of papers found, snowballing identified 83% of the papers in comparison to 46% of the papers for the database search. Snowballing failed to identify a few relevant papers, which potentially could have been addressed by identifying a more comprehensive start set. Conclusion: The efficiency of snowballing is comparable to database search. It can potentially be more reliable than a database search however, the reliability is highly dependent on the creation of a suitable start set.