Question

Carrying excess weight may have a greater impact on the risk for diabetes than it does on the risk for heart disease or early death, a new study has found.

To look at the effect of obesity independent of genetics, Swedish researchers followed 4,046 pairs of identical twins whose average age was 58. One of the twins was overweight, and the other was not. Since identical twins have the same genes, their weight difference could not be attributed to genetics.

After accounting for physical activity, smoking and educational level, the researchers found that having a higher body mass index, or B.M.I. — even among those in the obese range of 30 or higher — was not associated with an increased risk for heart attack or death. But a high B.M.I. was associated with an increased risk for diabetes.

“Based on these results, the association between obesity and cardiovascular disease is explained by genetic, not environmental, factors,” said the lead author, Peter Nordstrom, a professor of geriatric medicine at Umea University. “Unfortunately, this also means that environmental factors that reduce obesity do not reduce the risk of cardiovascular disease or death. But they most certainly decrease the risk for diabetes.”

1. What is the problem statement of the study? (10 points)

2 State the hypotheses in the study (10 points)

3. Identify the possible dependent, independent, and control/intervening variables (20 points)

4. Describe the data – identify the sample and the population (10 points

5. Is causality established in this case? Explain your answer. (10 points)

Answer 1

1. The study aims to look at the effect of obesity on the risk of diabetes, cardiovascular disease, and early death when this obesity is independent of genetics. When we say obesity is independent we mean obesity caused due to environmental factors instead of genetics.

2. Hypothesis: Obesity which is attributed to lifestyle or environmental factors and not to genetics increases the risk of diabetes. However, this kind of obesity has no effect on the risk of cardiovascular diseases or death.

3. Independent variables: The lifestyle status--exercise level, smoking, eating habits, and educational level and genetic information (genetic markers for risk of diabetes or cardiovascular diseases should also be included).
Dependent variables: Occurrence or development of (I) diabetes and (ii) cardiovascular disease.
Control: Data points that comprise a healthy environment and a healthy lifestyle. If a poor lifestyle increases the risk of diabetes then a good lifestyle should show a reduction in that risk. Since genetics plays a more important role in the risk of heart disease, a good lifestyle should not show a significant reduction in that risk compared to unhealthy or obese individuals.
The absence of genetic markers for cardiovascular disease should show a significant reduction in its occurrence.  

4. The data was collected from 4046 pairs of identical twins as it keeps the genetics of the pair of subjects the same for comparative study. The average age of the participants in this study was 58 years. One of the twins is obese. This can't be because of genetics because genetics is the same for both. So we sample environmental conditions such as physical activity level, smoking, eating habits, educational levels, etc. So, the environmental effects should be the cause of the obesity of one of the twins. The risk of developing diabetes and cardiovascular diseases is measured in the experiment.

5. From the details in the question, it doesn't appear that they checked for the presence of genetic markers and associated risk of getting cardiovascular disease. So, causation between genetics and risk of cardiovascular disease isn't tested and hence no causation can be established. Causation between environmental factors and obesity is established. Causality between obesity and risk of diabetes is established.