Relative Citation Ratio (RCR): A New Metric That Uses Citation Rates to Measure Influence at the Article Level
(A) Article citation rate (ACR) is calculated as the total citations divided by the number of years excluding the calendar year of publication (Supporting Equation S1 in S1 Text), when few, if any, citations accrue (S2 Fig). Numbers in the bars correspond to the number of citations in that year. (B) Box-and-whisker plots of 88,835 NIH-funded papers (published between 2003 and 2010), summarizing their ACR, journal impact factor (matched to the article’s year of publication), and field citation rate (FCR). Boxes show the 25th–75th percentiles with a line at the median; whiskers extend to the 10th and 90th percentiles. (C) Correlation of FCR as generated in 2012 versus 2 y later in 2014 for the same set of articles, as a function of the number of starting citations in 2012. Data were sliced by the number of initial citations in 2012, to assess stability as a function of the number of citing articles (and thereby the starting size of the network). Each point, correlation coefficient for >1,000 articles. Between 2012 and 2014, articles accrued a median of 5 additional citations. The inclusion of the full span of years ensures a representative spread of ACRs at each value of the independent axis. Furthermore, since papers in this analysis receive a nearly identical number of citations in their ninth year as in their first full year after publication (S2 Fig), the FCRs of articles published later in the chosen time frame (2003 to 2010) do not undergo substantially more change than those published earlier. (D) Generate an expectation for ACRs based on a preselected benchmark group, by regressing the ACR of the benchmark papers onto their FCRs (Supporting Equations S3, S4 in S1 Text), one regression each publication year. The graphed examples were sampled from a random distribution for illustrative purposes. (E) The coefficients from each year’s regression equation transforms the FCRs of papers published in the same year into expected citation rates (ECRs) (Supporting Equation S5 in S1 Text). Each paper’s RCR is its ACR/ECR ratio. A portfolio’s RCR is simply the average of the individual articles’ RCRs (Supporting Equation S6 in S1 Text).