A health worker is interested in determining if omega-3 fish oil can help reduce cholesterol in adults. She obtains permission to examine the health records of 200 people in a large medical clinic and classifies them according to whether or not they take omega-3 fish oil. She also obtains their latest cholesterol readings and finds that the mean cholesterol reading for those who are taking omega-3 fish oil is 18 points less than the mean for the group not taking omega-3 fish oil.

a. Is this an observational study or an experiment? Justify your answer.

b. Explain the concept of confounding in the context of this study and give one example of a variable that could be confounded with whether or not people take omega-3 fish oil.

c. Researchers find that the 18-point difference in the mean cholesterol readings of the two groups is statistically significant. Can they conclude that omega-3 fish oil is the cause? Why or why not?

Observational study

An experiment deliberately forces some treatment on individuals in arrangement to detect their responses. An observational study tries to store information without disturbing the scene they are noticing. The subjects were not given any treatment due to the data being based on health records and therefore the researchers had no control over who took and who did not take omega-3 fish oil. If the no treatment was assigned, the study is an observational study.

Two variables are confounded if their affect on a response variable cannot be discriminated from each other. The amount of exercise is a possible confounding variable.

Two variables are confounded when their affected on a response variable cannot be discriminated from each other. People who take omega-3 fish oil may be more interested in having a good health and therefore these people may exercise more. Although, the amount of exercise also affects of the amount of exercise is confounded with the omega-3 fish oil.

because there are possible confounding variables

The conclusion from the previous part is that the study would be an observational study and that the study had possible confounding variables. As long as there are possible confounding variables which cannot be $100\%$assure that the omega-3 fish oil is the reason of the statistically significant difference.