Although the Sex Discrimination Act (1975) made it unlawful to purposefully discriminate against women, imbalances may arise from hiring and promotion decisions unconsciously based on stereotypes about inherent differences between men and women’s traits and abilities. These stereotypes create gender roles which prescribe types of work that men and women are suitable for. Role Incongruity theory (Eagly & Karau, 2002) posits that people associate leadership with men, and that the feminine gender role is perceived as a poor fit with leadership requirements.  This leads to a preference for men in high-status roles, and even when women reach these, their behaviour is negatively evaluated, although identical behaviour might be praised in a man (Eagly & Karau, 2002). Quotas could therefore increase diversity by bypassing this prejudiced selection process (Crosby, Iyer, & Sincharoen, 2006).

Furthermore, quotas may eliminate these gender roles altogether, because experience of working with women who disprove the stereotype of poor leadership tends to reduce people’s biases (Dasgupta & Asgari, 2004). One ecologically valid study (De Paola et al., 2010) looked at the effects of applying gender quotas to elections for Italian municipalities – such a policy was in place for two years before being repealed. Representation of women in politics increased in municipalities with elections during the quota period, and this effect persisted for years after the abolition of quotas. A similar reduction in stereotypes has also been shown in Indian village councils (Beaman, Chattopadhyay, Duflo, Pande, & Topalova, 2009). This suggests a long-term benefit from quotas.

Beaman, L. A., Chattopadhyay, R., Duflo, E., Pande, R., & Topalova, P. (2009, November). Powerful women: Does exposure reduce bias? Quarterly Journal of Economics, 124(4), 1497–1540.
Crosby, F. J., Iyer, A., & Sincharoen, S. (2006). Understanding affirmative action. Annual Review of Psychology, 57, 585–611. doi: 10.1146/annurev.psych.57.102904.190029.
Dasgupta, N., & Asgari, S. (2004). Seeing is believing: Exposure to counterstereotypic women leaders and its effect on the malleability of automatic gender stereotyping. Journal of Experimental Social Psychology, 40(5), 642–658. doi: 10.1016/j.jesp.2004.02.003.
De Paola, M., Scoppa, V., & Lombardo, R. (2010). Can gender quotas break down negative stereotypes? Evidence from changes in electoral rules. Journal of Public Economics, 94(5), 344–353.
Eagly, A. H., & Karau, S. J. (2002). Role congruity theory of prejudice toward female leaders. Psychological Review, 109(3), 573–598. doi: 10.1037//0033-295X.109.3.573.