Consider the model below, where x1 is an indicator variable for sex with female as baseline (i.e., 1=male, 0=female), x2 and x3 are indicator variables for drug groups A and B, respectively, with group C as the baseline, and Y is the extent of recovery (1, 2, . . ., 5), with 5 corresponding to most recovery. You may refer to this model as the "current" model.

If a likelihood ratio test (LRT) of the drug is desired, what model in addition to the current model would be involved? Which model is H0, and which is Ha? What are the degrees of freedom for the test?