Discussion:
Q: A researcher hypothesizes that the lowering in cholesterol associated with weight loss is really due to exercise. To test this, the researcher carefully controls for exercise while comparing the cholesterol levels of a group of subjects who lose weight dieting with a control group that does not diet. The difference in mean cholesterol levels between groups is not significant. Can the researcher claim that weight loss has no effect? What statistical analysis could the researcher use to make his or her case more strongly?