Keywords: Bibliometrics, gender differences, ranking universities, research productivity.THE representation of women in research varies across countries, institutions and disciplines. However, the fact of their underrepresentation is undeniable. Only four (Portugal, Estonia, Slovak Republic and Iceland) of the 28 OECD nations whose data are available show representation of women greater than 40%, with a maximum of 46% (ref. 1). This phenomenon is underlain by a mix of different factors, with different weights across countries: educational emancipation has come later for women, with consequent lesser numbers of potential candidates for academic positions; lesser interest among women for research activity; the scientific production of women tends to be lower than that for men, perhaps due to the social roles of women as wives and mothers, or from causes of gender discrimination; gender discrimination can also occur in recruitment processes. One way to reduce the underrepresentation of women in research is to control for the factors exogenous to scientific merit in all processes of comparative performance evaluation at the individual and institutional levels. By doing so one can avoid incorrect conclusions and choices that are harmful to women and to those institutions with greater female representation in their research staff. In this regard it is important to note that the so-called 'productivity gap' in favour of men is a documented fact. The lower research performance of women has been established in several studies from diverse countries and disciplines 2-6 , although it is decreasing over time [7][8][9][10][11][12] , and it is more visible in the early stages of career 13 and among top scientists 14,15 . Looking at productivity as indicated by patenting, women faculty members contribute about 40% compared to men 16 . There is equally substantial literature investigating the possible causes of the productivity gap, particularly the issues of the environmental and personal factors that can influence the performance of a researcher, beyond the personal merit of the individual 17 . Rossiter 18 indicates the particular case of the so called 'Matilda effect', which occurs when female scientists are not recognized in the bylines of the publications resulting from joint research. A separate concern is that in the career recruitment stages, the percentage of women applicants who are successful in selection procedures is generally low 19 . In the subsequent stages of entry to the academic environment, females generally evaluate their mentors as less satisfactory than do their male colleagues 20 . However, there is also no doubt that the changing personal conditions that the researchers experience over time also affect their productivity. In the late postdoctoral and early faculty years, many qualified women scientists stop applying for NIH grants 21 . During their careers, women present lower productivity in the intermediate levels of seniority 22 . In this phase, marriage and school-going children have negative effect...