A comparison of 17 author-level bibliometric indicators for researchers in Astronomy, Environmental Science, Philosophy and Public Health in Web of Science and Google Scholar

Author-level bibliometric indicators are becoming a standard tool in research assessment. It is important to investigate what these indicators actually measure to assess their appropriateness in scholar ranking and benchmarking average individual levels of performance. 17 author-level indicators were calculated for 512 researchers in Astronomy, Environmental Science, Philosophy and Public Health. Indicator scores and scholar rankings calculated in Web of Science (WoS) and Google Scholar (GS) were analyzed. The indexing policies of WoS and GS were found to have a direct effect on the amount of available bibliometric data, thus indicator scores and rankings in WoS and GS were different, correlations between 0.24 and 0.99. High correlation could be caused by scholars in bottom rank positions with a low number of publications and citations in both databases. The hg indicator produced scholar rankings with the highest level of agreement between WoS and GS and rankings with the least amount of variance. Expected average performance benchmarks were influenced by how the mean indicator value was calculated. Empirical validation of the aggregate mean h-index values compared to previous studies resulted in a very poor fit of predicted average scores. Rankings based on author-level indicators are influenced by (1) the coverage of papers and citations in the database, (2) how the indicators are calculated and, (3) the assessed discipline and seniority. Indicator rankings display the visibility of the scholar in the database not their impact in the academic community compared to their peers. Extreme caution is advised when choosing indicators and benchmarks in scholar rankings.