Is the Previously Reported Increase in Second- and Higher-order Birth Rates in Norway and Sweden from the mid-1970s Real or a Result of Inadequate Estimation Methods?

According to models estimated separately for second-, third-, and fourth-birth rates in Norway, an increase took place from the mid-1970s to about 1990, given age and duration since last previous birth. A similar rise in the birth rates was seen in Sweden, except that the upturn at short durations was sharper. It is shown in this study, using Norwegian register data, that the increase partly reflects earlier changes in lower-order parity transitions. When models for each parity transition are estimated jointly, with a common unobserved factor included, there is no longer an upward trend in Norwegian second-birth rates, but a very weak decline, and the increase in the higher-order birth rates is strongly reduced compared to that found in the simpler approach.