Loads of special authorship functions: Linear growth in the percentage of “equal first authors” and corresponding authors

We show that between 1999 and 2008 the percentage of articles with more than one corresponding author or with several authors that contributed equally, leading to so-called “equal first authors,” has steadily been on the rise. Increasing numbers of corresponding authors and equally contributing authors may lead to increased stress on teamwork if not properly acknowledged in research evaluation exercises.