posted by phia
A nutritionist wants to conduct a study to validate the efficacy of an herb as an aid in weight loss. She randomly assigns half of a group of overweight persons to a treatment group who are given the herb with instructions for its use and a planned diet for six weeks. The other half of the group is given parsley with the same instructions and same diet. A nurse at the nutrition center weighs each subject on Friday of each week. Select the potential source of confounding.
A. Placebo effect
B. Experimenter effect
C. Method of assignment to treatment and control groups
D. The study is essentially free of potential confounding.
My answer is B, but I think it could also be D