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The questions on fertility that are usually asked in censuses provide data on both recent births and lifetime fertility. In the 1960s Brass and colleagues observed that these data are typically affected by common errors. In particular, reports on recent births tend to be misreported by mothers of all ages, the consequence of a combination of reference period errors (respondents interpreting the reference period to be other than the interval actually asked about) and omission of neonatal deaths.

Women’s reports of their number of children ever born also tend to be too low. Here the effect is is believed to become worse with increasing age. The reasons advanced for this bias include age exaggeration among teenage mothers, omission of dead children, and omission of older children who have left home. Over-reporting of children ever born may result from the misrepresentation of fostered children as ‘own’ children, or from confusion of still births with live births.

This section describes the investigations that should be pursued in the evaluation and assessment of fertility data collected in a census. The sections describe