Google Scholar as a source for scholarly evaluation: a bibliographic review of database errors

Google Scholar (GS) is an academic search engine and discovery tool launched by Google (now Alphabet) in November 2004. The fact that GS provides the number of citations received by each article from all other indexed articles (regardless of their source) has led to its use in bibliometric analysis and academic assessment tasks, especially in social sciences and humanities. However, the existence of errors, sometimes of great magnitude, has provoked criticism from the academic community. The aim of this article is to carry out an exhaustive bibliographical review of all studies that provide either specific or incidental empirical evidence of the errors found in Google Scholar. The results indicate that the bibliographic corpus dedicated to errors in Google Scholar is still very limited (n=49), excessively fragmented, and diffuse; the findings have not been based on any systematic methodology or on units that are comparable to each other, so they cannot be quantified, or their impact analysed, with any precision. Certain limitations of the search engine itself (time required for data cleaning, limit on citations per search result and hits per query) may be the cause of this absence of empirical studies.