Biofeedback training is often used to help people who suffer migraine headaches. A recent study found that 29 out of 50 participants reported a decrease in the frequency and severity of their headaches after receiving biofeedback training. Of the remaining participants in this study, 10 reported that their headaches were worse, and 11 reported no change.
a. Discard the zero-difference participants, and use a sign test with α = .05 to determine whether the biofeedback produced a significant difference.
b. Divide the zero-difference participants between the two groups, and use a sign test to evaluate the effect of biofeedback training.