Period measures of fertility are distorted by changes in the timing (tempo) of fertility. These measures are exaggerated when the age at childbearing is falling. They are also underestimated when couples are postponing childbearing. Iran has experienced a rapid decline in its fertility and a rise in age at marriage and childbearing for last two decades. This paper aims to measure the effect of changes in the timing of childbearing (tempo effect) on total fertility rate in Iran.
The paper uses 2 percent sample data from Iran's 2006 Population and Housing Census. Discrete-time survival models are used to construct fertility life tables which estimate Parity Progression Ratios (PPR) and Total Fertility Rate for the period 2004-06. These models yield probabilities of having a first/next birth by parity and duration in parity. Tempo-adjusted total fertility rates are then calculated by using the formula suggested by Bongaarts and Feeney. The results show conventional methods underestimate fertility measures for the 3-year period due to changes in the timing of fertility in Iran.