Effects of previous birth interval length on child outcomes can be estimated in a sibling analysis even when there are only two siblings.
Øystein KravdalPublished in: Paediatric and perinatal epidemiology (2020)
It is good news that families with only two children can contribute to the estimation of birth interval effects. This is because, with a broader basis for the estimation, the precision is improved and there is less reason for concern about the general relevance of the estimates. An important limitation, however, is that it is potentially problematic to control for maternal age in a sibling model estimated only for the first and second child.