Commentary on van Raalte et al.'s "The Dangers of Drawing Cohort Profiles From Period Data: A Research Note".

van Raalte et al. (2023) alerted demographers to the potential dangers of calculating cohort measures from the "diagonals" of gridded age-period (AP) data. In the case of cohort fertility, however, a minor change to the estimation procedure can mitigate the trend and cohort size biases that the authors identify. With an appropriate algorithm, researchers can estimate cohort fertility indices from AP data quite well.