The estimation of the genetic correlation: the use of the jackknife

To understand fully the process of evolution of quantitative traits it is necessary to be able to estimate the genetic correlation and its associated standard error. At present, estimation methods are available only for relatively simple designs. An alternative procedure is to use the correlation of family means as an estimate of the genetic correlation. We evaluate the utility of the family mean method and that of the more general procedure, the jackknife. The family mean method is shown to be potentially very biased unless family sizes are very large (≈ 20), and therefore its general utility is questionable. However, the jackknife method does provide valid estimates of both the correlations (phenotypic and genetic) and their standard errors.