a, b Area-normalised histograms of citations (a) and the publishing journal’s impact factor (IF, b) of all papers from different African and non-African regions, as indicated. In each case, all citations above ≥95, and IF above ≥9.5 were allocated to a single bin (top). c Citations plotted against IF for every paper in the database (small grey dots), and for means by country (large dots), as indicated. Linear correlation coefficients as indicated. Source data are provided as a Source Data file.