Search Engine Overlaps : Do they agree or disagree?

Secondary studies, such as systematic literature reviews and mapping studies, are an essential element of the evidence-based paradigm. A critical part of the review process is the identification of all relevant research. As such, any researcher intending to conduct a secondary review should be aware of the strengths and weakness of the search engines available. Analyse the overlap between search engine results for software engineering studies. Three independent studies were conducted to evaluate the overlap between multiple search engines for different search areas. The findings indicate that very little overlap was found between the search engines. To complete a systematic review, researchers must use multiple search terms and search engines. The lack of overlap might also be caused by inconsistent keyword selection amongst authors.