Replacement of parents by meritorious offspring in within-family selection

In within-family selection it may be advantageous not to replace a parent automatically by the best offspring of the same sex but, if necessary, to postpone such replacement until there is a group with a sufficiently meritorious offspring. Roux (1983, Biometrics 39, 479-483) studied this option by an approximate approach. When exact methods are used instead, substantially lower values of selection gain due to the option are obtained. It is concluded that the option is advantageous only under rather restricted circumstances.