Table 3 also provides a note of caution for our results. The three columns under the Basic Model header summarize comparisons of the base model with each of the heterogeneity models using a likelihood ratio test. For the tabulated traits, all heterogeneity models reject the base model (number of asterisks represents the p-value at which base model is rejected). In contrast, the next four columns, which compare a model with heterogeneity in both genetic and environmental variances to more parsimonious models, show that, quite often, multiple models with intermediate levels of heterogeneity give a similar fit to the most general heterogeneity model considered. For example, for the cardiovascular trait peak systolic velocity (PSV), both models with heterogeneity only in environmental variance and models with heterogeneity in the total variance fit as well as the model with full heterogeneity (p > 0.05, indicating no significant degradation in fit when using the parsimonious models). Thus, there was clear evidence for heterogeneity in variance components by sex, but it was difficult to decide whether the heterogeneity was due to genes, environment, or both.
