"The groups observed that the disparity of spaceflight data available for men and women who have flown in space – 477 men vs. 57 women as of June 2013 – makes it difficult to derive concrete conclusions based on sex and gender alone."<p>Statistics can't work like that, can it? It's surely <i>not</i> harder to derive concrete conclusions from a large, imbalanced 477-57 group than from a smaller but balanced 57-57 group... right?<p>At the extreme, you could always take a random subsample of 57 men.<p>Note: I agree that imbalance is bad, I just disagree that it's bad for taking the conclusions listed in the article and other similar conclusions.