Abstract
Widely used standard expressions for the sampling variance of intraclass correlations and genetic correlation coefficients were reviewed for small and large sample sizes. For the sampling variance of the intraclass correlation, it was shown by simulation that the commonly used expression, derived using a first-order Taylor series performs better than alternative expressions found in the literature, when the between-sire degrees of freedom were small. The expressions for the sampling variance of the genetic correlation are significantly biased for small sample sizes, in particular when the population values, or their estimates, are close to zero. It was shown, both analytically and by simulation, that this is because the estimate of the sampling variance becomes very large in these cases due to very small values of the denominator of the expressions. It was concluded, therefore, that for small samples, estimates of the heritabilities and genetic correlations should not be used in the expressions for the sampling variance of the genetic correlation. It was shown analytically that in cases where the population values of the heritabilities are known, using the estimated heritabilities rather than their true values to estimate the genetic correlation results in a lower sampling variance for the genetic correlation. Therefore, for large samples, estimates of heritabilities, and not their true values, should be used.
Full Text
The Full Text of this article is available as a PDF (119.0 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Koots K. R., Gibson J. P. Realized sampling variances of estimates of genetic parameters and the difference between genetic and phenotypic correlations. Genetics. 1996 Jul;143(3):1409–1416. doi: 10.1093/genetics/143.3.1409. [DOI] [PMC free article] [PubMed] [Google Scholar]