General instructions:
Please complete the following assignment corresponding to Parts 3 & 4 of Bias in Epidemiological Studies by no later than Monday, November 30th at 11pm SAST/12am EAT.
At the end of the assignment we ask you to please note 1) approximately how much time you spent on the homework and how much time you spent reviewing the materials (videos and learning checks) , 2) what questions, if any, you have from the videos and/or any places you might have gotten stuck in the assignment, and 3) provide your feedback on the this week’s content and materials. Thank you once again for your assistance in completing these additional questions!
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Question 1 of 20
1. Question
1. In a case-control study of prostate cancer, cases are less likely to be detected in the base population if they are exposed than if they are unexposed. Assuming no other sources of bias, we would expect the estimated rate ratio, comparing exposed with unexposed subjects, to be:
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Question 2 of 20
2. Question
Investigators conducted an observational study of sleep disorders and the risk of developing diabetes among patients attending a cardiology clinic that monitors their medications for their cardiovascular disease (CVD). Diabetes and heightened psychological stress are independent risk factors for developing cardiovascular disease and stress is associated with a higher risk of developing a sleep disorder.
2. Which of the DAGs below represents the study that the investigators conducted, with the DAG drawn under the assumption of no causal effect of exposure on outcome?
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Question 3 of 20
3. Question
In the previous homework, we discussed the paper by Susser et al. (1996)that reported a positive association between prenatal famine and risk of Schizophrenia in the Dutch famine birth cohort. Below is an extract from the discussion of the paper.
“The live births of the EX2 cohort represent conceptions that survived difficult circumstances. It has been suggested that the persistence of schizophrenia, despite reduced fertility and survival among cases, may be explained if genes that increase the risk for schizophrenia also confer a selective advantage in some other area. Possibly EX2 births were selected for some genetic factor that is associated with better survival from conception to birth but that is also associated with an increased risk for schizophrenia.”
(“EX2 cohort” refers to the exposed group, who were conceived at the height of the famine. You may read the original paper for more information.)
3. Please draw a DAG based on the information above and upload here.
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Question 4 of 20
4. Question
4. Following from Question 3, briefly explain how selection bias may be a problem in the study.
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Question 5 of 20
5. Question
5. Suppose you are interested in conducting a case-control study to replicate the association between prenatal nutritional deficiency and risk of Schizophrenia reported in the Dutch famine birth cohort. Briefly describe how you would select cases and controls, and any potential selection bias that may be introduced by your selection of controls.
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Question 6 of 20
6. Question
6. Please describe how you can measure prenatal nutritional deficiency in the case-control study you proposed in Question 5, and any potential information bias that may be introduced by your measurement.
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Question 7 of 20
7. Question
Please answer Questions 7-12 based on the following information:
A researcher decided to conduct a randomized trial among current students to assess the effect of a mindfulness/meditation intervention on psychological stress measured with a standardized questionnaire. Students who enrolled in the study were more likely to practice yoga than non-participants and were also more likely to be vegetarian than students who did not volunteer to participate in the study. Practicing yoga is known to reduce stress as measured with the standardized questionnaire used as the endpoint for this study. Assume that vegetarianism is not associated with stress and that there is perfect compliance with the assigned treatment arm (i.e., all students randomized to the mindfulness/meditation intervention did so, and students randomized to not practice mindfulness/meditation did not).
7. Draw and upload a DAG based on the paragraph above to show the relationship between baseline yoga, vegetarianism, selection into the study, post-randomization mindfulness/mediation, and psychological stress at the end of the study.
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Question 8 of 20
8. Question
8. Based on the DAG you drew, are you concerned that confounding in this study can lead to invalid estimates of the effect of the mindfulness/meditation intervention on stress as measured in this study? Why or why not?
If confounding is a concern, which variables would need to be adjusted for in the analysis to attain a valid estimate of the relationship between the mindfulness/meditation intervention and psychological stress?
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Question 9 of 20
9. Question
9. Are you concerned that there is selection bias arising from the inclusion of only students that volunteered to participate in the study? Why or why not?
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Question 10 of 20
10. Question
After the students were enrolled in the study, those who were randomized to not receive the mindfulness/meditation intervention were more likely to drop out of the study and be censored (lost to follow-up). Furthermore, students who practiced yoga at baseline were less likely to drop out of the study and be censored.
10. Draw and upload a new DAG that incorporates the previous information and also includes the additional information regarding loss to follow-up.
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Upload your answer to this question.
This response will be reviewed and graded after submission.
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Question 11 of 20
11. Question
11. Based on the new DAG, are you concerned that confounding in this study can lead to invalid estimates of the effect of the mindfulness/meditation intervention on stress as measured in this study? Why or why not?
If confounding is a concern, which variables would need to be adjusted for in the analysis to attain a valid estimate of the relationship between the mindfulness/meditation intervention and psychological stress?
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This response will be reviewed and graded after submission.
Grading can be reviewed and adjusted.Grading can be reviewed and adjusted. -
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Question 12 of 20
12. Question
12. Are you concerned that there is selection bias arising from loss to follow-up? Why or why not?
If selection bias is a concern, can it be mitigated by conditioning on any variables described in this scenario?
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Question 13 of 20
13. Question
How much time did you spend on this homework?
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Question 14 of 20
14. Question
Please include here any questions from the recorded lectures or homework that you would like to be addressed during the lab session.
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Question 15 of 20
15. Question
Your feedback is important to us. So that we can adequately adjust the lecture materials, please answer the questions below relating to each of this week’s topics:
Part 3: Selection Bias
Was the amount of information presented too little, just right, or too much?
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Question 16 of 20
16. Question
The lecture’s contents were clearly explained.
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Question 17 of 20
17. Question
How was the pace of the lecture?
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Question 18 of 20
18. Question
Part 4: Information Bias
Was the amount of information presented too little, just right, or too much?
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Question 19 of 20
19. Question
The lecture’s contents were clearly explained.
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Question 20 of 20
20. Question
How was the pace of the lecture?
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