What these three figures mean
A journal's 2-year impact pools everything it published. These three split that figure by what was published. Articles are ordinary research papers. Reviews survey a field and are cited far more heavily than research papers almost everywhere, so a journal that publishes many of them carries a headline impact its research papers alone would not support. Communications are short reports. Comparing the three shows how much of the headline figure rests on review content — the single largest reason two journals with the same impact factor are not comparable.
