Multiple Citation Indicators and Their Composite across Scientific Disciplines

Many fields face an increasing prevalence of multi-authorship, and this poses challenges in assessing citation metrics. Here, we explore multiple citation indicators that address total impact (number of citations, Hirsch H index [H]), co-authorship adjustment (Schreiber Hm index [Hm]), and author order (total citations to papers as single; single or first; or single, first, or last author). We demonstrate the correlation patterns between these indicators across 84,116 scientists (those among the top 30,000 for impact in a single year [2013] in at least one of these indicators) and separately across 12 scientific fields. Correlation patterns vary across these 12 fields. In physics, total citations are highly negatively correlated with indicators of co-authorship adjustment and of author order, while in other sciences the negative correlation is seen only for total citation impact and citations to papers as single author. We propose a composite score that sums standardized values of these six log-transformed indicators. Of the 1,000 top-ranked scientists with the composite score, only 322 are in the top 1,000 based on total citations. Many Nobel laureates and other extremely influential scientists rank among the top-1,000 with the composite indicator, but would rank much lower based on total citations. Conversely, many of the top 1,000 authors on total citations have had no single/first/last-authored cited paper. More Nobel laureates of 2011–2015 are among the top authors when authors are ranked by the composite score than by total citations, H index, or Hm index; 40/47 of these laureates are among the top 30,000 by at least one of the six indicators. We also explore the sensitivity of indicators to self-citation and alphabetic ordering of authors in papers across different scientific fields. Multiple indicators and their composite may give a more comprehensive picture of impact, although no citation indicator, single or composite, can be expected to select all the best scientists.Citation indicators addressing total impact, co-authorship, and author positions offer complementary insights about impact. This article shows that a composite score including six citation indicators identifies extremely influential scientists better than single indicators.Author Summary: Multiple citation indicators are used in science and scientific evaluation. With an increasing proportion of papers co-authored by many researchers, it is important to account for the relative contributions of different co-authors. We explored multiple citation indicators that address total impact, co-authorship adjustment, and author order (in particular, single, first, or last position authorships, since these positions suggest pivotal contributions to the work). We evaluated the top 30,000 scientists in 2013 based on each of six citation indicators (84,116 total scientists assessed) and also developed a composite score that combines the six indicators. Different scientists populated the top ranks when different indicators were used. Many Nobel laureates and other influential scientists rank among the top 1,000 with the composite indicator, but rank much lower based on total citations. Conversely, many of the top 1,000 authors on total citations had no single/first/last-authored cited paper. More Nobel laureates are among the top authors when authors are ranked by the composite score than by single indicators. Multiple indicators and their composite give a more comprehensive picture of impact, although no method can pick all the best scientists.