A study by Meltzer et al. (A-27) examined the response to 5 mg desloratadine, an H1-receptor antagonist, in patients with seasonal allergies. During the fall allergy season, 172 subjects were randomly assigned to receive treatments of desloratadine and 172 were randomly assigned to receive a placebo. Subjects took the medication for 2 weeks after which changes in the nasal symptom score were calculated. A significant reduction was noticed in the treatment group compared to the placebo group, but gender was not a significant factor. What are the factors in the study? At how many levels does each occur? What is the response variable?