scenarios on the future balance between men and women is negligible (see Table 3.6). The sex ratio was favorable to females in 1995 and is expected to remain so throughout the projection period. In 1995, there was 0.954 male per female; put another way, the population was 51.1 percent female. By 2050, the ratio is expected to change slightly, to 50.9 percent female. The range of variation in the sex ratios across our alternative immigration assumptions varies only between 0.963 and 0.966.²⁶

Throughout the next century, males will outnumber females before middle age because more boys than girls are born. After age 50, the relatively higher mortality of men decreases their ratio to women and eventually results in a markedly higher number of women at the older ages. None of these age patterns in the sex ratio will be altered, no matter which immigration assumption prevails.

In contrast to the situation for sex composition, immigration will significantly affect the age structure of the future population. As Chapter 2 demonstrates, immigrants are concentrated in the age groups from 20 to 40 and are relatively scarce in the over-60 group. In the zero-migration assumption, the population will be much older than it would be if current immigration persists. Thus, the aging of the population, which is already obvious, would become even more pronounced if immigration stopped altogether.

Perhaps the single most common index of population aging is the median age of the population—the age that divides the younger half of the population from