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
Since assignment is random, it is not C.
I choose A and it was incorrect
To determine the potential source of confounding in the given study, we need to understand what confounding refers to. Confounding occurs when the association between an independent variable (in this case, the herb or parsley) and a dependent variable (weight loss) is influenced by another variable that is related to both the independent and dependent variables.
In this study, the potential source of confounding is the method of assignment to the treatment and control groups (option C). The nutritionist randomly assigned participants to either the treatment group or the control group. However, random assignment alone may not be sufficient to eliminate potential confounding.
For example, if the treatment group had a higher proportion of participants who were more motivated to lose weight compared to the control group, we might observe more significant weight loss in the treatment group. In that case, the difference in weight loss might not be solely due to the herb or parsley but rather to the differing levels of motivation in the two groups.
To minimize this potential confounding, the randomized controlled trial should ensure that the assignment process is truly random, such as using a computer-generated randomization sequence or random number table. Additionally, it is important to consider factors like age, gender, or previous weight loss attempts and distribute them equally between the treatment and control groups.
The other options provided are not sources of potential confounding in this study:
A. The placebo effect refers to the psychological and physiological effects that occur when a person receives a placebo (inert substance or treatment) but believes it to be active. However, since both treatment groups receive some substance (herb or parsley), the placebo effect is not a potential source of confounding.
B. The experimenter effect refers to unintended actions, behaviors, or expectations of the researcher that can influence the participants' behavior or response. While it is essential for the researcher to standardize the instructions and procedures, this is not a potential source of confounding in this study.
D. The study being "essentially free of potential confounding" is an incorrect option since we have identified the potential source of confounding (option C).
Therefore, the correct answer is C: Method of assignment to treatment and control groups.