Tempo and the TFR

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Description/Abstract

The paper proposes that whether period indicators are biased by timing effects depends on the objective of measurement. Several kinds of bias in the TFR are identified. Five reasons for measuring period fertility are distinguished: to explain fertility time trends, to anticipate future prospects, to describe trends, to provide input parameters for formal models, and to communicate with non-specialist audiences. Genuine timing effects are not biasing where period fertility is the explanandum, but are distorting where the aim is to estimate cohort fertility. Synthetic measures such as the TFR have a number of known defects. Alternatives to the TFR are available, and seem a more defensible solution to current problems than tempo adjustment. Tempo adjustment could be more fruitfully considered a form of modelling rather than empirical measurement. The measurement of period fertility could benefit by a more statistical approach and less reliance on indicators requiring stable assumptions.