Researchers conducted a randomized, double-blind, clinical trial in which some patients with schizophrenia were given the drug clozapine and others were given haloperidol. After one year 61 of 163 patients in the clozapine group showed clinically important improvement in symptoms, compared with 51 out of 159 in the haloperidol group. Identify the type of statistical method that is appropriate for these data, but do not actually conduct the analysis.