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.

Answer : C

Don't repeat questions. It wastes our time responding to multiples. See your later post.

To identify the potential source of confounding in this study, we need to consider factors that could impact the outcome but are unrelated to the herb being tested. In this case, the potential source of confounding is the method of assignment to treatment and control groups, which is option C.

Confounding occurs when there is a disturbance in the relationship between the treatment (herb) and the outcome (weight loss) due to the influence of a third variable. In this study, the nutritionist randomly assigns half of the group of overweight persons to the treatment group (herb) and the other half to the control group (parsley). However, if there is any bias or flaw in the randomization process, it may lead to an imbalance in the characteristics or behaviors of the participants across the treatment and control groups.

For example, if the nutritionist did not ensure proper randomization and accidentally assigned more individuals with a higher basal metabolic rate to the treatment group, then the observed weight loss in the treatment group might be due to their higher metabolic rate rather than the herb itself.

Therefore, the method of assignment to treatment and control groups is the potential source of confounding in this study.