Though women earn almost half of the PhDs in geoscience, they only hold 10 percent of the tenured faculty positions in this field. A recent paper published in Nature Geoscience takes a look at the career pipeline that feeds researchers into these positions, finding that women receive fewer excellent recommendation letters than their male colleagues. This is likely to be one of the factors holding women back at this critical time in their careers.

Under-representation of women in STEM disciplines is well documented, and the disparity tends to increase in the years between postdoctoral positions and faculty positions. Previous research on this phenomenon has focused on everything from implicit bias to historical, social, and institutional factors.

This most recent study focused on the role of recommendation letters, which are an important part of academic advancement. They often help labs and institutions determine if the “fit” is right for an applicant. Previous studies have shown that there is evidence of qualitative differences in recommendation letters for men versus women, but this new study focuses specifically on the issue of overall “tone” in the recommendations.

The sample used in the study comprised 1,224 recommendation letters written for 452 applicants to post-doctoral positions, 70 percent of them for women. There were a total of approximately 1,100 recommenders, 12 percent of whom were women, 88 percent men. (105 recommenders wrote recommendations for more than one applicant.)

The researchers used two statistical models (fixed effects hierarchical linear models, to be exact) to examine the relationship between applicant gender and letter length. Neither of these two models showed a significant correlation between applicant gender and recommendation letter length—the recommendation letters were roughly the same length, regardless of the applicant’s gender.

Next, they looked at the relationship between applicant gender and letter tone, using three similar models. They found that, after controlling for regional variation, recommender gender, and letter length, female applicants were significantly less likely to receive an excellent recommendation compared to males. Obviously, this could have significant consequences for their job prospects.

This study provides more insight into the pipeline leaks that prevent more women from achieving faculty positions after their doctoral work, although there are limitations to its scope. For example, the researchers were unable to control for the possibility that the female applicants were actually less qualified than their male counterparts. They were also unable to measure the strength of the relationship between the applicant and the recommender, which would obviously influence the letters’ contents.

Despite these limitations, the study does provide some insight into another mechanism that might be contributing to the imbalance of men and women in advanced academic positions.

Nature Geoscience, 2016. DOI: 10.1038/NGEO2819 (About DOIs).