Author ordering and citation-based measures of scholarly impact: Implications for research assessment.

OBJECTIVE: To assess the use of common author ordering conventions, their effects on measures of citation impact, and their implications for the assessment of individual researchers and researcher rankings. DESIGN: Analysis of associations between the use of author ordering conventions, measures of citation impact, and researcher rankings using publications by Canadian primary health care researchers included in the Scopus database. SETTING: Canada. PARTICIPANTS: The 49 living Canadian primary health care researchers with the most first-author citations. MAIN OUTCOME MEASURES: Spearman rank correlations were assessed between rankings based on number of first-author citations and alternative measures of number of citations. Changes in researcher rankings were assessed based on alternative citation metrics. RESULTS: Rank order correlations varied from 0.55 (first author vs h index) to 0.83 (first-author citations vs first- and second-author citations). The proportion of researchers whose rankings changed by 12 or more ranks (25% or greater absolute change) compared to rankings based on first-author citations varied from 14% for rankings based on first- and second-author citations to 51% for rankings based on h index. CONCLUSION: The variability and inconsistency of author ordering thwart efforts to identify or create valid measures to rank citation impact. Adoption of author ordering based on contribution as a universal convention would enhance the reliability and validity of comparisons and rankings across disciplines and research fields and would facilitate comparisons among candidates for hiring, tenure, promotion, and awards.