Sex Ratio

The sex ratio (SR) is the most popular index of sex composition used in demographic and other scholarly analyses; it is defined as the number of males per 100 females:

An SR above 100 indicates an excess of males, and an SR below 100 indicates an excess of females. In some countries including India, Iran, Pakistan, and Saudi Arabia, the SR is calculated as the number of females per 100 males, but the SR formula shown above is used by most demographers and international bodies such as the United Nations.

Henry Shryock, Jacob Siegel, and Associates have noted that SRs of nations are usually around 95 to 102 unless some major loss of life affects the country. A national SR lower than 90 or higher than 105 is extreme.

Marcia Guttentag and Paul Secord's Too Many Women? The SR Question is the best accounting of the SR in historical populations. In high SR societies, young adult women are decidedly valued. [Page 1448]They might be permitted to choose their own marriage partners or to marry into superior socioeco-nomic classes. High SR societies might promote sexual morality, in particular the virginity of potential brides and the fidelity of women in marriage. Some cultures tend to endorse sexual exclusivity and love on the part of both sexes, while others accept promiscuity and infidelity on the part of men.

Many of the characteristics of low SR societies are the opposite of those in high SR societies. Women are likely regarded as sex objects, feeling immobilized and devalued by the society. Due to their oversupply, they are rarely able to marry into higher socioeconomic classes. Greater numbers of men and women tend to remain single, and those who marry are more prone to get divorced.

Most societies have SRs at birth (SRBs) between 104 and 106. This so-called biologically normal SRB is likely an evolutionary adaptation to the fact that females have higher survival probabilities than males. Since at every year of life males have higher age-specific death rates than females, slightly more males than females are required at birth for there to be around equal numbers of males and females when the groups reach their marriageable ages.

Biology thus dictates that the age-specific SR will be highest at the very young ages and should then decline with age, attaining a value of around 100 for persons in their late 20s and continuing to decline to levels around 50 or 60 in the oldest ages.

Dudley Poston and Karen Glover have shown that the SRB in the United States is invariant, at about 105 for every year. In contrast, China had an SRB only slightly above 107 in 1980, a ratio which began to increase in the late 1980s, reaching 115 in 1990, 120 in 2000, and 118 in 2005. This has occurred in China (and in Taiwan, South Korea, India, and several other Asian countries) for three main reasons: (1) fertility has declined very rapidly in China from six children per woman in the 1960s to around 1.7 at the start of the new millennium; (2) China is characterized by a Confucian patriarchal tradition where son preference is strong and pervasive. When Chinese women were having six children on average, the probability was very low (less than 2 percent) that none of the six children would be male. By comparison, Gilles Pison has written that when women have between one and two children, the probabilities are between 25 and 50 percent; and (3) ultrasound technology enabling the prenatal determination of sex has been widely available in China since the 1980s; thus, many Chinese use this technology to identify the sex of the fetus, and in many instances, if it is a female fetus, to then abort it.

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