  Science is becoming increasingly more interdisciplinary, giving rise to more
diversity in the areas of expertise within research labs and groups. This also
have brought changes to the role researchers in scientific works. As a
consequence, multi-authored scientific papers have now became a norm for high
quality research. Unfortunately, such a phenomenon induces bias to existing
metrics employed to evaluate the productivity and success of researchers. While
some metrics were adapted to account for the rank of authors in a paper, many
journals are now requiring a description of the specific roles of each author
in a publication. Surprisingly, the investigation of the relationship between
the rank of authors and their contributions has been limited to a few studies.
By analyzing such kind of data, here we show, quantitatively, that the
regularity in the authorship contributions decreases with the number of authors
in a paper. Furthermore, we found that the rank of authors and their roles in
papers follows three general patterns according to the nature of their
contributions, such as writing, data analysis, and the conduction of
experiments. This was accomplished by collecting and analyzing the data
retrieved from PLoS ONE and by devising an entropy-based measurement to
quantify the effective number of authors in a paper according to their
contributions. The analysis of such patterns confirms that some aspects of the
author ranking are in accordance with the expected convention, such as the fact
that the first and last authors are more likely to contribute more in a
scientific work. Conversely, such analysis also revealed that authors in the
intermediary positions of the rank contribute more in certain specific roles,
such as the task of collecting data. This indicates that the an unbiased
evaluation of researchers must take into account the distinct types of
scientific contributions.
