Question

AP2.22. 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 lower than the mean for the group not taking omega-$3$ fish oil.
(a) Is this an observational study or an experiment? Explain.
(b) Do these results provide convincing evidence that taking omega-$3$ fish oil lowers cholesterol?
(c) Explain the concept of confounding in the context of this study and give one example of a possible confounding variable.

Short answer

(a) The study is observational.

(b) The results do not provide convincing evidence that taking omega- $3$fish oil lowers cholesterol.

(c) Two variables are confounded when their effects on a response variable cannot be distinguished. One example for possible confounding variable is the amount of exercise.

Step-by-step solution

Part (a) Step 1: Given information

The health records of $200$people in a large medical clinic and classifies, according to whether or not they take omega -$3$fish oil. To explain the observational study or an experiment.

Part (a) Step 2: Explanation

In the given data, an experiment gradually sets some treatments on people to monitor their comebacks. An observational analysis attempts to collect data without bothering the scene.
No treatments were allocated to the $200$people as the information is founded on health records and the researchers didn't include any control over who took the omega-$3$fish oil and who didn't. As no treatments were given.

Hence, the study is observational.

Part (b) Step 1: Given information

The mean cholesterol reading for those who are taking omega-$3$fish oil is $18$points lower than the mean for the group not taking omega-$3$fish oil. To explain those results provide evidence that taking omega-$3$ fish oil lowers cholesterol.

Part (b) Step 2: Explanation 

A health worker is experimenting with discovering if omega- $3$fish oil can help reduce cholesterol levels in adults or not. As no treatments were assigned the study is observational.

Since there are possible confounding variables we cannot be $100\%$sure that the omega- $3$fish oil is the cause of the statistically significant difference can be other factors influencing the outcome.

Hence, these results do not provide convincing evidence that taking omega- $3$ fish oil lowers cholesterol.

Part (c) Step 1: Given information

To explain the concept of confounding in the context of the study and give one example of a possible confounding variable.

Part (c) Step 2: Explanation

In this study, two variables are confounded when their effects on a response variable cannot be distinguished from each other. People who take omega-$3$fish oil might be more curious in maintaining good health and these people might exercise more.

The amount of exercise also affects our cholesterol levels and cannot distinguish the effects of the amount of exercise from the omega-$3$-fish oil, which indicates that the portion of exercise is confounded with the omega-3 fish oil.
Hence, two variables are confounded when their effects on a response variable cannot be distinguished from each other.

One example for possible confounding variable is the amount of exercise.