Epidemiology - Ch. 10

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

Blinding

True/False: Restriction attempts to ensure equal distribution of the confounding variable in each exposure category.

False; prevention

Selection bias is a form of bias that occurs because of the influence of study results on the chance of publication.

False; publication bias

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?

Selection bias: survival bias

The strategy that is not aimed at reducing selection bias is:

Standardized protocol for structured interviews

Confounding is the distortion if the estimate of the effect of an exposure of interest because it is mixed with the effect of an extraneous factor.

True

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.

True

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?

[all are correct]: The severity (stage) of disease of the patients at the two hospitals at baseline, the starting point of the one-year follow-up at both hospitals (after operation versus after discharge), difference in the postoperative care at the two hospitals, equally thorough follow-up for mortality

Factors that contribute to random error include:

[all are correct]: poor precision, sampling error, and variability in measurement.

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

[all are correct]: use memory aids and validate exposure, provide standardized training sessions and protocols, use standardized collection forms and try to ensure all questions are clearly understood

The purpose of a double-blind study is to:

avoid observer and interviewee 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:

improve the likelihood that the two groups will be comparable with regard to known and unknown confounding factors.

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:

is a factor associated with physical activity and heart disease

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

neither observers nor subjects know which subject receives the vaccine and which receives a placebo.

True/False: A study is said to have internal validity when there has been proper selection of study groups and a lack of error in measurement.

true