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 the same diet without the herb. A nurse at the nutrition center weighs each subject on Friday of each week. Select the potential source of confounding.
A. The placebo effect
B. Method of assignment to treatment and control groups
C. Experimenter effect
D. The study is essentially free of confounding sources
is it B
I disagree.
An independent variable is the potential stimulus or cause, usually directly manipulated by the experimenter, so it could also be called a manipulative variable.
A dependent variable is the response or measure of results.
Extraneous variables — other than the independent variable — potentially can affect the dependent variable, so they must be controlled. If possible, you try to keep them constant between the experimental and control group.
The experimental group receives the independent variable.
The control group is similar to experimental, except it does not receive the independent variable. Extraneous variables are balanced between experimental and control groups.
well it can't be D or A placebo because it refers to the situation in which patients improve simply because they believe they are receiving a useful treatment.
im left with C
How does the experimenter affect the study?
1. Single blind gives the control group a placebo — a substance that is inert, it has no physical effect. Subjects don't know if they are in experimental or control group to reduce placebo effect, a change in behavior solely due to believing that you are getting the independent variable.
2. Double blind keeps both subjects and experimenter ignorant of group setup. Distribution of the independent variable and placebo are controlled by third party. This controls for experimenter bias and self-fulfilling prophecy, which means that experimenters with particular expectations are likely to consciously or unconsciously to bias the experiment and influence it to conform to their expectations.
As an example, suppose you want to find out if fluorides reduce dental cavities. You would find two groups, trying to control the extraneous variables. Extraneous variables are found by surveying previous research in the area. In this case, you would match the groups in terms of previous history of cavities, diet and dental hygiene habits including how and how often they brush their teeth.
The experimental group would get toothpaste with the independent variable, the fluoride, while the control group would not have the fluoride in their toothpaste. The toothpaste without the fluoride would be the placebo.
The dependent variable would be the number of cavities after participating in the experiment for a time. The dependent variable indicates the results, but it is not the results. At the end of the experiment, both groups could have no change in cavities or one of the groups could have a greater reduction in cavities. (Of course, if the fluoride increased cavities, you wouldn't want to use it.) All of these varied results would be indicated in terms of the dependent variable.
If only the subjects do not know who is getting the fluoride, it is a single blind experiment. If both the subjects and experimenter do not know, it is a double blind.
Yes, you are correct. The potential source of confounding in this study design is the method of assignment to treatment and control groups, which is option B.
The reason for this is that the nutritionist randomly assigned participants to the treatment or control group. Random assignment helps to minimize the differences between the two groups, making it more likely that any observed differences in weight loss can be attributed to the herb rather than other factors. However, it is still possible that there could be some imbalances or differences between the two groups that could confound the results. For example, if the nutritionist did not properly randomize and assign participants, there could be a systematic difference in certain characteristics between the two groups that could affect weight loss outcomes.
The other options are not considered potential sources of confounding in this specific study design.
- The placebo effect (option A) is not relevant here because both groups are receiving a treatment, one with the herb and one without it. The placebo effect refers to when participants experience a perceived improvement or change due to their belief in receiving a treatment, even if the treatment itself has no active effect.
- The experimenter effect (option C) refers to when the experimenter's expectations or actions unintentionally influence the study outcomes. While this is a potential source of bias in research, it is not directly related to the assignment of participants to treatment or control groups.
- Option D suggests that the study is essentially free of confounding sources, which is not true since the method of assignment can introduce confounding if not properly conducted.