Sunday, 22 November 2015

The gender bias in economics

A fair amount has been written over the last couple of weeks about gender bias in economics. This Justin Wolfers piece in the New York Times was one of the catalysts, and it was followed up by Dan Diamond at Forbes and Jeff Guo at the Washington Post. The storm has been mostly about the new paper by Anne Case and Angus Deaton, which has more often than not been reported as a Deaton paper, with Case mentioned almost as an afterthought (so it's worth noting that Anne Case is a well-respected economics professor at Princeton in her own right).

Tyler Cowen at Marginal Revolution then pointed to this new paper by Heather Sarsons (a PhD candidate at Harvard, where I am based for the next month), entitled "Gender differences in recognition for group work" (which was also reported on by Jeff Guo in his article). In the paper, Sarsons first notes that there is a well-established literature noting that women are less likely to be promoted than men, and that "over 30% of the observed gap in tenure rates can not be accounted for by observable productivity differences or family commitments". She then looks specifically at tenure decisions for economics faculty, testing whether co-authoring of papers prior to tenure decisions has different effects for male and female academic economists.

The choice of economics as the field to study is deliberate. In many fields, the order of authorship in co-authored papers is meaningful - the first author was often the largest contributor, the second author was the second-largest contributor, and so on (how 'large' relative contributions are is open to negotiation, I guess). In contrast, in economics it is more likely that co-authors appear in alphabetical order, regardless of the merit of their relative contributions [*]. So, while in other fields the order of authors' names provides a signal of their relative contributions to co-authored papers, this typically isn't the case for economics. Sarsons's hypothesis is that this leads employers (universities) to have to make judgment calls about the relative contributions of the co-authors, and that these judgment calls tend to go against women (because the employers' prior belief is that female economists are lower quality than male economists).

Using data from 552 economists over the period 1975 to 2014, she first finds that:
Approximately 70% of the full sample received tenure at the first institution they went up for tenure at but this masks a stark difference between men and women. Only 52% of women receive tenure while 77% of men do. There is no statistically significant difference in the number of papers that men and women produce although men do tend to publish in slightly better journals...
An additional paper is associated with a 5.7% increase in the probability of receiving tenure for both men and women but a constant gender gap between promotion rates persists. Women are on average 18% less likely to receive tenure than a man, even after controlling for productivity differences. 
So, women received tenure at a lower rate than men, but why? The total number of papers they publish is no different and doesn't make a difference to the probability of tenure, and the difference in paper quality is actually rather small (even though it is statistically significant). Turning to her specific hypothesis about co-authorship, she finds that:
an additional coauthored paper for a man has the same effect on tenure as a solo-authored paper. An additional solo-authored paper is associated with a 7.3% increase in tenure probability and an additional coauthored paper is associated with an 8% increase.
For women, a sole-authored paper has an effect that is not statistically significantly different from that for men, but the effect of an additional co-authored paper is nearly 6 percentage points lower (i.e. a 2% increase, rather than an 8% increase, in the probability of receiving tenure).

To test the robustness of her findings, she does a similar analysis with sociologists (where the social norm is authorship by order of relative contributions), and finds no significant differences in tenure decisions between men and women. She concludes:
The data are not in line with a traditional model of statistical discrimination in which workers know their ability and anticipate employer discrimination...
The results are more in line with a model in which workers do not know their ability or do not anticipate employer discrimination, and where employers update on signals differently for men and women.
So, there is a bias against women. How far does this bias extend? There is a conventional wisdom that men are more suited for economics than women (to which I say: they should attend one of my ECON110 classes, where the female students are more often than not at the top of the class). This recent paper by Marianne Johnson, Denise Robson, and Sarinda Taengnoi (all from University of Wisconsin Oshkosh) presents a meta-analysis of the gender gap in economics performance at U.S. universities. Meta-analysis involves combining the results of many previous studies to generate a single (and usually more precise) estimate of the effect size. It (hopefully) overcomes the biases inherent in any single study, such as the study of gender gaps in economics performance.

In the paper, the authors [**] take results from 68 studies, containing 325 regressions. They find a number of things of note:
...only 30.7% of regressions actually conform to the conventional wisdom - that men statistically significantly outperform women... In 9.2% of regressions, we find that women performed statistically significantly better...
Notable is the increase in regressions that find that women outperforming [sic] men after 2005...
We find a negative coefficient on year, which would indicate that the performance gap is narrowing over time, regardless of whether we use the year of data collection or the year of publication as our time measure.
So, the observed performance gap is declining over time. Which brings me back to Sarsons's paper. She used data from 1975 to 2014, which is a wide span of time, over which things have gotten better for female academics (surely?). I wonder what happens if she accounts for year of tenure? I doubt the effect goes away, but at least we might know a bit more about the changes over time and if indeed things are getting better.

[Update: I just had one of those wake-up-and-realise-you-said-something-wrong moments. Sarsons does include year fixed effects in her econometric model, so is already controlling for changes over time somewhat, but not changes in the difference in tenure probability between men and women over time (which would involve interacting that fixed effect with the female dummy or with one or more of the other variables in her model)].

[HT: Shenci Tang and others]


[*] There are many exceptions to this co-authoring rule. My rule-of-thumb in co-authoring is that the first author is the one whose contributions were the greatest, with all other authors listed alphabetically.

[**] All women co-authors, which relates to the Sarsons's paper, since one of her other results was that co-authoring with other women didn't result in as large a penalty as co-authoring with men.

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