Table 1.
Typical characteristics of academic citation databases and search engines.
Table 2.
Systematic reviews (SRs) used as case studies and their search strings (along with modifications to WoS search strings necessary to function in Google Scholar advanced search facility as indicated by strikethrough text).
Searches were performed on 06/02/15. Web of Science includes the following databases as part of the MISTRA EviEM subscription; KCI-Korean Journal Database, SciELO Citation Index and Web of Sciences Core Collection.
Fig 1.
Proportion of total a) full text and b) title Google Scholar search results by literature type for 7 case studies (see Table 2 for descriptions of SR codes).
Table 3.
Overlap between Web of Science (WoS) and Google Scholar (GS) for title searches in Web of Science and the first 1,000 search results from title searches in Google Scholar.
See Table 2 for case study explanations.
Table 4.
Overlap between Web of Science (WoS) and Google Scholar (GS) for topic word searches in Web of Science and the first 1,000 search results from full text searches in Google Scholar.
n/a corresponds to search results that were too voluminous to download in full. See Table 2 for case study explanations.
Table 5.
Duplication rates (proportion of total results that are duplicates) for Google Scholar and Web of Science for title-level, topic word and full text searches using 7 case study systematic review search strings.
Numbers in parentheses correspond to the standard deviations of the individual case study duplication rates. Sample size refers to the number of search records in total, followed by the number of independent search strings (i.e. the number of case studies investigated).
Table 6.
Duplication rates (proportion of total results that are duplicates) in Google Scholar and Web of Science searches across the 7 case studies.
Duplication rates are assessed for up to 1,000 search records (or the total number where less than c. 1,300). For Web of Science the full text results were ordered by publication date (newest first) and relevance where more than 1,000 results were returned. Numbers are duplication rate (%) followed by total search records in parentheses.
Table 7.
The ability of Google Scholar to find included articles from six published systematic reviews.
Records identified as citations are found only within reference lists of other articles (their existence is not verified by the presence of a publisher version or full text article, unlike hyperlinked citations).