P.Mean: Can an outcome with three levels be used in logistic regression (created 2008-09-18).

I had a quick question about logistic regression. Is this the appropriate test to use when your outcome variable has 3 levels? For example, we are looking at factors associated with obesity in children. Our outcome variable is BMI percentage and is classified as either normal, at risk, or overweight. I ran logistic regression on SAS and then realized this may not be the right test to run.

It has been a while since I have used SAS, but it you used PROC LOGISTIC with a three level outcome variable, it should either provide you with a warning/error message or switch you automatically to a different procedure. In your case, BMI category ordinal. At risk is clearly between normal and overweight. Any categorical variable that allows ordered comparisons (larger than, smaller than, in between) is ordinal.

There is a procedure, ordinal logistic regression, that works very well with this type of data. I'm planning to include a simple example of ordinal logistic regression on my new website, but it may be a while..
