Open and closed birth intervals for once-married spouse-present white women.

Using the 1970 1/1,000 Public Use Sample of the U.S. population, the relationships of the closed and open birth intervals with parity and mother's age, with parity and marital duration, and with children ever born/marital duration and mother's age are analyzed. These findings both replicate and expand on Srinivasan's earlier research on the open interval. The open interval is more sensitive as an index of marital fertility when marital duration and parity are controlled than when mother's age and parity are controlled.