This chapter describes theory and methods for measuring mean changes in phenotypes when the phenotypic variable is considered as a latent construct with multiple indicators. Data for exposition of the methods are generated using EQS simulation techniques. Two datasets are used, one simulating the population prior to a selection event, the pre-selection group, and another simulating the population after the selection event, the post-selection group. The example includes an environmental construct that may also influence phenotypic variable means. The example demonstrates how structural equation modeling (SEM) may be used to statistically control for such environmental influences to arrive at a more accurate estimate of the effect of the selection event. Data are analyzed with LISREL version 8.30. The analysis includes a measurement model and stacked model of covariances to test model assumptions, and a final means model to estimate the mean phenotypic response to selection.