Do hot peppers relieve pain? A researcher claims that the chemical capsaicin, the ingredient that makes chili peppers hot, helps relieve pain. He randomly assigns subjects with chronic back pain to two groups. In one group he injects capsaicin near the sciatic nerve. In the other he injects a placebo.

The subjects were blinded as to the treatment they received, but the researcher knew which treatment each subject received. After an hour, the researcher interviewed subjects and rated the change in pain they experienced based on comments from the subjects during the interview. Critics said that the results were suspect because the ratings were not blind. Explain what this means and how lack of blindness could bias the reported results.

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