One of the most egregious manifestations of gender bias is the phenomenon of “missing women.” The number of missing women is projected to increase to 150 million by 2035, as a result of prenatal sex selection and excess female mortality relative to men, and is reflected in male-biased sex ratios at all ages. The economics literature identifies several proximate causes of the deficit of females, including the widespread use of prenatal sex selection in many Asian countries, which has been fueled by the diffusion of ultrasound and other fetal sex-detection technology. The use of prenatal sex selection has become even more expansive with a decline in fertility, as parents with a preference for sons are less likely to achieve their desired sex composition of children at lower levels of fertility. Gender discrimination in investments in health and nutrition also leads to excess female mortality among children through multiple channels.

The deeper causes of son preference lie in the socioeconomic and cultural norms embedded in patriarchal societies, and recent literature in economics seeks to quantify the impact of these norms and customs on the sex ratio. Particularly important are the norms of patrilineality, in which property and assets are passed through the male line, and patrilocality, in which elderly parents coreside with their sons, whereas their daughters move to live with their husbands’ families after marriage. Another strand of the literature explores the hypothesis that the devaluing of women has roots in historical agricultural systems: Societies that have made little use of women’s labor are today the ones with the largest female deficits. Finally, economic development is often associated with a decline in son preference, but, in practice, many correlates of development, such as women’s education, income, and work status, have little impact on the sex ratio unless accompanied by more extensive social transformations.

A number of policies have been implemented by governments throughout the world to tackle this issue, including legislative bans on different forms of gender discrimination, financial incentives for families to compensate them for the perceived additional costs of having a daughter, and media and advocacy campaigns that seek to increase the inherent demand for daughters by shifting the norm of son preference. Quantitative evaluations of some of these policies find mixed results. Where policies are unable to address the root causes of son preference, they often simply deflect discrimination from the targeted margin to another margin, and in some cases, they even fail in their core objectives. On the other hand, the expansion of social safety nets has had a considerable impact in reducing the reliance of parents on their sons. Similarly, media and advocacy campaigns that aim to increase the perceived value of women have also shown promise, even if their progress appears slow. Analysis of the welfare consequences of such interventions suggests that governments must pay close attention to underlying sociocultural norms when designing policy.