Question 1

The purpose of matching in a case-control study is to select the controls in such a way that the control group has the same distribution as the cases with respect to certain confounding variables.

Accepted Answer

Matching in a case-control study is used to ensure that the control group is similar to the case group in terms of specific confounding variables, which helps to isolate the effect of the exposure being studied.

Question 2

In a study to determine the incidence of a chronic disease, 150 people were examined at the end of a three-year period. Twelve cases were found, giving a cumulative risk of 8%. Fifty other members of the initial cohort could not be examined; 20 of these 50 could not be examined because they died. Which source of bias may have affected the study?
A) Information bias: interviewer/abstractor bias
B) Hawthorne effect
C) Selection bias: survival bias
D) Information bias: recall bias

Accepted Answer

The study may have been affected by selection bias, specifically survival bias, because the 20 individuals who died could have had the disease, and their absence from the final examination could skew the results.

Question 3

You are investigating the role of physical activity in heart disease and suggest that physical activity protects against having a heart attack. While presenting these data to your colleagues, someone asks if you have thought about confounders such as factor X. This factor X could have confounded your interpretation of the data if it:
A) is a factor for some other disease, but not heart disease.
B) is a factor associated with physical activity and heart disease.
C) is a part of the pathway by which physical activity affects heart disease.
D) has caused a lack of follow-up of test subjects.

Accepted Answer

A confounder is a variable that is associated with both the exposure (physical activity) and the outcome (heart disease), potentially distorting the observed relationship.

Question 4

Which of the following is not a method for controlling the effects of confounding in epidemiologic studies?
A) Randomization
B) Stratification
C) Matching
D) Blinding
E) Restriction

Accepted Answer

Blinding is a method used to prevent bias in studies by keeping participants, investigators, or assessors unaware of the group assignments, but it does not control for confounding.

Question 5

The purpose of a double-blind study is to:
A) achieve comparability of cases and controls.
B) reduce the effects of sampling variation.
C) avoid observer and interviewee bias.
D) avoid observer bias and sampling variation.
E) avoid interviewee bias and sampling variation.

Accepted Answer

A double-blind study is designed to prevent both the participants and the experimenters from knowing who is receiving a particular treatment, which helps to eliminate observer and interviewee bias.

Question 6

Which of the following is a technique to reduce information bias?
A) Use memory aids and validate exposures.
B) Provide standardized training sessions and protocols.
C) Use standardized collection forms.
D) Try to ensure that questions are clearly understood.
E) All are correct.

Accepted Answer

All the options listed are techniques to reduce information bias by ensuring accurate and consistent data collection and interpretation.

Question 7

An epidemiologic experiment is performed in which one group is exposed to a suspected factor and the other is not. All individuals with an odd hospital admission number are assigned to the second group. The main purpose of this procedure is to:
A) ensure a double-blind study.
B) prevent observer bias with respect to the factor.
C) prevent observer bias with respect to the outcome.
D) improve the likelihood that the two groups will be comparable with regard to known and unknown confounding factors.
E) guarantee comparability of the two groups with regard to other relevant factors.

Accepted Answer

Random assignment, such as using odd or even numbers, helps ensure that the groups are comparable with regard to confounding factors, both known and unknown.

Question 8

A double-blind study of a vaccine is one in which:
A) the study group receives the vaccine and the control group receives a placebo.
B) neither observers nor subjects know the nature of the placebo.
C) neither observers nor subjects know which subject receives the vaccine and which receives a placebo.
D) neither the study group nor the control group knows the identity of the observers.
E) the control group does not know the identity of the study group.

Accepted Answer

In a double-blind study, neither the participants (subjects) nor the researchers (observers) know who is receiving the actual treatment and who is receiving the placebo, to prevent bias in the results.

Question 9

Surgeons at Hospital A report that the mortality rate at the end of a one-year follow-up after a new coronary bypass procedure is 15%. At Hospital B, the surgeons report a one-year mortality rate of 8% for the same procedure. Before concluding that the surgeons at Hospital B have vastly superior skill, which of the following possible confounders would you examine?
A) The severity (stage) of disease of the patients at the two hospitals at baseline
B) The starting point of the one-year follow-up at both hospitals (after operation versus after discharge)
C) Difference in the postoperative care at the two hospitals
D) Equally thorough follow-up for mortality
E) All are correct.

Accepted Answer

All the listed factors could potentially confound the comparison of mortality rates between the two hospitals.

Quiz 10: Data Interpretation Issues

The purpose of matching in a case-control study is to select the controls in such a way that the control group has the same distribution as the cases with respect to certain confounding variables.

Which of the following is not a method for controlling the effects of confounding in epidemiologic studies?

The purpose of a double-blind study is to:

Which of the following is a technique to reduce information bias?

An epidemiologic experiment is performed in which one group is exposed to a suspected factor and the other is not. All individuals with an odd hospital admission number are assigned to the second group. The main purpose of this procedure is to:

A double-blind study of a vaccine is one in which: