6 Models for nominal outcomes with case-specific data
An outcome is nominal when the categories are assumed to be unordered. For example, marital status can be grouped nominally into the categories of divorced, never married, married, or widowed. Occupations might be organized as professional, white collar, blue collar, craft, and menial, which is the example we use in this chapter. Other examples include reasons for leaving the parents' home, the organizational context of scientific-work (e.g., industry, government, and academia), and the choice of language in a multilingual society. Further, in some cases a researcher might prefer to treat an outcome as nominal, even though it is ordered or partially ordered. For example, if the response categories are strongly agree, agree, disagree, strongly disagree, and don't know, the category "don't know" invalidates models for ordinal outcomes. Or, you might decide to use a nominal regression model when the assumption of parallel regressions is rejected. In general, if you have concerns about the ordinality of the dependent variable, the potential loss of efficiency in using models for nominal outcomes is outweighed by avoiding potential bias.