A METHOD FOR ASSESSING EXTENT AND SOURCES OF HETEROGENEITY OF RESIDUAL VARIANCES IN MIXED LINEAR-MODELS

A statistical method is presented for identifying sources of heterogeneity of residual variance in mixed linear models. The method is based on a log-linear model for the residual variances from which parameters can be estimated and hypotheses tested using the marginal likelihood function. It can be viewed as a generalization of Bartlett's test. Computing procedures are presented and an illustration is given. The method can be used with experimental or field data, e.g., to detect possible preferential treatment of daughters of sires or to investigate the possible segregation of major genes. © 1990, American Dairy Science Association. All rights reserved.