A systematic lack of data on men. Science has systematically accumulated data that is asymmetric across the sexes: the overwhelming majority of mouse experiments are done only in female mice for simplicity. Despite efforts like the NIH\u2019s \u201CSex as a Biological Variable\u201D effort, that encouraged scientists to do experiments in both male and female mice, there continues to be a huge imbalance in favor of collecting data only on female model organisms to be consistent with the literature.