Twenty-two percent of the active astronaut corps are women (35 of 158). The average female astronaut is 42 years old (vs. 43 years for men) and weighs 60.7 kg (vs. 81.2 kg for men). Insufficient data exist in most of the discipline areas at the present time to draw valid conclusions about gender-specific differences in astronauts or to determine their impact on the health of male and female astronauts. The inability to draw statistical comparisons based on gender differences is linked to the small number of female astronauts, resulting in an insufficient study sample. In addition, individual differences in physiological responses within genders are usually as large as, or larger than, differences between genders, so individual characteristics usually outweigh gender differences per se.