Prediction of response to selection within families

The distinction is clarified between two different uses of the term 'within-family selection', either to imply that one individual of each sex is selected from each family or to imply that individuals are selected on their deviation from family mean, in which case families may not be equally represented. In the short term, selection on within-family deviation is expected to give higher responses, but in the long term, selection within families is expected to give higher responses as the effective population size is larger. The two schemes are the same, however, if only two individuals of each sex are recorded in each family.