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Chapter 7: Q. 2.22 (page 491)

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?

Short Answer

Expert verified
  1. Observational study
  2. Two variables are confused when their effects on a response variable cannot be distinguished. The amount of exercise may be a complicating variable.
  3. No, due to the possibility of confounding variables.

Step by step solution

01

Part (a) Step 1: Given information

A health professional wants to know if omega-3 fish oil can help adults lower their cholesterol. She gets authorization to look through the medical records of 200 people at a large medical clinic and classify them based on whether or not they take omega-3 fish oil. She also collects their most recent cholesterol measurements and discovers that individuals who take omega-3 fish oil have a mean cholesterol reading that is 18 points lower than those who do not.

02

Part (a) Step 2: Explanation

An experiment purposely administers some therapy to participants in order to detect their responses. An observational research attempts to record information without disturbing the scene being observed. Because the data was based on health records, the individuals were not provided any treatment, and the researchers had no control over who took and who did not take omega-3 fish oil. The study is an observational study if no therapy was assigned.

03

Part (b) Step 1: Given information

A health professional wants to know if omega-3 fish oil can help adults lower their cholesterol. She gets authorization to look through the medical records of 200 people at a large medical clinic and classify them based on whether or not they take omega-3 fish oil. She also collects their most recent cholesterol measurements and discovers that individuals who take omega-3 fish oil have a mean cholesterol reading that is 18 points lower than those who do not.

04

Part (b)  Step 2: Explanation

The effects of two factors on the same response variable are said to be confused when they can't be distinguished. Omega-3 fish oil users may be more concerned about their health and, as a result, exercise more. Although the quantity of exercise has an impact on omega-3 fish oil levels, the amount of exercise has an impact on omega-3 fish oil levels.

05

Part (c) Step 1: Given information

A health professional wants to know if omega-3 fish oil can help adults lower their cholesterol. She gets authorization to look through the medical records of 200 people at a large medical clinic and classify them based on whether or not they take omega-3 fish oil. She also collects their most recent cholesterol measurements and discovers that individuals who take omega-3 fish oil have a mean cholesterol reading that is 18 points lower than those who do not.

06

Part (c) Step 2: Explanation

The study would be an observational study with possible confounding variables, according to the previous section's conclusion. As long as confounding variables exist, it is impossible to be 100 percent certain that omega-3 fish oil is the cause of the statistically significant difference.

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