IBM® SPSS® Amos™ 28

With two categories, there is only one category boundary. Following the same reasoning given in the section Choosing boundaries when there are three categories, the value of that category boundary can be assigned arbitrarily for models that are location and scale-invariant (Browne, 1982, pp. 75-77) .

Amos assigns the value 0 to the category boundary for two-category variables. To assign a different value, click the Details button in the Data Recode window.

A model that is identified when all its measured variables are numerical can become unidentified if one of those measured variables is an ordered-categorical variable with two categories. Although fixing that variable's single category boundary to a constant is enough to determine the variable's location, its scale (i.e., its unit of measurement) remains indeterminate. Just as it is typically necessary to impose two constraints on the model parameters in order to fix the location and scale of an unobserved variable, it is typically necessary to impose one parameter constraint in order to fix the scale of an ordered-categorical variables that has two categories. This issue is addressed under the topic, Parameter identification with dichotomous variables.