As the article itself states: > Experiments and retrospective field studies each have advantages. The advantage of experiments is that they can more confident

As the article itself states: > Experiments and retrospective field studies each have advantages. The advantage of experiments is that they can more confidently infer cause and effect by isolating gender as the predictor variable. The advantage of retrospective field studies is that they tend to have higher ecological validity because they are conducted in real-world situations. In this paper, we use a retrospective field study as a first step to quantify the effect of gender bias in open source. The research is presented in context, an important and valid context, too. At the end, they discuss potential explanations and never go so far as to say "And all of this is clearly because ______". A controlled study would be a great followup, but I'd sure put stock in these compelling and well documented findings.