Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
Scand J Public Health. 2010 Jun;38(4):426-33. doi: 10.1177/1403494810364682. Epub 2010 Mar 9.
The most commonly used indicator of fertility, the period total fertility rate (TFR(p)), tends to underestimate actual fertility when women delay childbearing. The objective of this study was to examine to which extent fluctuations in Danish fertility rates result from changes in timing of births and, thus, whether the conventional TFR(p) is a distorted indicator of fertility quantum. In addition, we investigated whether such changes in timing explained the observed regional differences in the TFR(p) in Denmark.
The study applied age-, period-, county-, and parity-specific data from the Danish Fertility of Women and Couples Dataset, 1980-2001. We evaluated fluctuations in period fertility rates by the tempo-adjusted TFR(') - a proposed variant of the conventional TFR(p) taking period changes in timing of births into account. Tempo-effects were given by the difference between TFR(p) and TFR(') , and these period measures were compared to actual cohort fertility.
Mean age at childbearing increased with more than 3 years over the period 1980-2001 leading to considerable differences between TFR(p) and TFR(' ) . A tempo-effect of up to 0.347 children per woman was observed. Comparisons with actual cohort fertility showed consistency with the TFR('). However, tempo-adjustment did not attenuate observed regional differences.
This study indicates that the conventional TFR(p) consistently underestimates the fertility quantum in periods characterized by changes in timing of births, and that the TFR(' ) generally provides good indication of actual cohort quantum for the period in question. Considerable tempo-effects were observed within counties; however, differences between regions were not explained by changes in timing of births.
生育力最常用的指标——总生育率（TFR(p)）在女性生育延迟时往往会低估实际生育率。本研究旨在探讨丹麦生育率波动在多大程度上是由生育时间变化引起的，以及传统的 TFR(p) 是否是生育数量的扭曲指标。此外，我们还研究了这种生育时间的变化是否解释了丹麦 TFR(p)观察到的区域差异。
该研究应用了 1980-2001 年丹麦妇女和夫妇生育力数据集的年龄、时期、县和生育次数特定数据。我们通过调整生育时间的 tempo-adjusted TFR(')评估时期生育率的波动，这是一种考虑生育时间变化的传统 TFR(p)的变体。时期效应由 TFR(p)和 TFR(')之间的差异给出，这些时期指标与实际队列生育率进行了比较。
1980-2001 年期间，生育年龄平均增加了 3 年以上，导致 TFR(p)和 TFR(')之间存在显著差异。观察到的 tempo 效应高达每个女性 0.347 个孩子。与实际队列生育率的比较表明，TFR(')具有一致性。然而，tempo 调整并没有减弱观察到的区域差异。
本研究表明，在生育时间变化的时期，传统的 TFR(p)始终低估了生育数量，而 TFR(')通常为所研究时期的实际队列数量提供了良好的指示。在县内观察到相当大的 tempo 效应；然而，区域差异不能用生育时间的变化来解释。
