A question that often arises when examining group differences on a variable is if any observed differences are due to differences in the groups themselves or differences in the instrument(s) used to measure the variable. One of the more useful ways of answering this question is by assessing invariance in LVs. To do so, however, requires I adjust the LVM I introduced in Chapter 3 to include both covariances and means, which is why these models are sometimes referred to as mean and covariance structure (MACS) models. A MACS path model is shown in Figure 4.1.