On the method of Penrose of estimating the number of effective factors contributing to a character.

Penrose (1969) presented a method of estimating the number of effective factors contributing to a quantitative character. The method uses samples of parent-child and sib-sib phenotypic values. More detailed mathematical analysis shows that his assertions regarding the method are correct under the assumptions which he made, provided that his phrase 'the same quantitative effect' is interpreted to mean 'makes an equal contribution to the variance'.