The probability of being a first-born has fluctuated consider-ably since 1940. During the 1940s almost 40 percent of all white births were first-borns; the proportion for nonwhites was between 25 percent and 30 percent. Subsequently, first-order births declined in relative importance for both races,
reaching a low point in the late 1950s and early 1960s. Thereafter the proportion rose rapidly, especially for nonwhites; by 1975 it was well over 40 percent for both races. At the opposite end of the birth-order distribution the reverse pattern prevailed. The proportion of births that were fourth-order or above rose in the 1950s and then declined very sharply in the 1960s and 1970s,