In a study of the effectiveness of an anti-psychotic drug, patients treated with the drug were compared to patients receiving a placebo. In terms of the number relapsing, 698 of 1,068 patients relapsed after taking the placebo while 639 out of 2,127 patients relapsed after taking the anti-psychotic drug. Test the prediction that the anti-psychotic is significantly more effective in preventing relapse than the placebo.