Question

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? 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?

Answer 1

Answer:

1. Observational study
2. See explanation below
3. No

Explanation:

1. This is an observational study as the health worker did not conduct any experiment but instead, she observed and studied patients data and drew her inferences from the available data.
2. A confounding is an external variable in an experiment that can change the effect of the dependent and independent variable. They can ruin an experiment if not accounted for and suggest false correlations, and introduce bias as it is one of the sources of bias in epidemiological studies. For example, using the study above, it is said that the cholesterol reading of the group not taking omega-3 fish oil is 18 points higher than the other; a confounding variable would be like an extra independent variable unaccounted for which could influence the outcome of the study like the age of the patients, family history, diet etc. All these extra variables can influence the cholesterol level of the patients but yet were unaccounted for and if inferences are made from the observations, the correlations could be false.
3. Even though the 18 point difference is statistically significant, they cannot conclude that omega-3 fish oil is the cause because of the effect of confounding in experiments and the many external variables like lifestyle, diet, smoking etc. which could influence the outcome of the research that were unaccounted for