We randomly divide 200 volunteers with headaches into two groups who take identical-looking pills. One group gets a homeopathic remedy and the other a placebo. After 20 minutes we ask them to rate their headache pain as "no change", "somewhat better", "much better", or "gone". What is the appropriate test?
◦ 2-proportion z-test
◦ χ2 test of homogeneity
◦ 2-sample t-test
◦ matched pairs t-test
◦ χ2 test of independence