Selection bias is most likely to occur in which

12 Jun Selection bias is most likely to occur in which

Question
Question 1
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Selection bias is most likely to occur in which type of study?Answer
Prospective cohort studies
Retrospective cohort studies
Case­control studies
Both retrospective cohort and case­control studies

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2 points

Question 2
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A case­control study is being conducted where 10% of the cases and controls actually had the
exposure of interest. However, when asked about the exposure, only 7% of each group recalled the
exposure correctly. This inaccuracy, represented equally between cases and controls, could be called:

Answer
Differential misclassification bias
Nondifferential misclassification bias
Surveillance bias
Selection bias

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2 points

Question 3
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When assessing the results of a study, what are the possible explanations for the observed results?
Answer
The observed results may be due to chance (i.e., random error)
The observed results may be true
The observed results may be due to bias
The observed results may be due to confounding
The 3rd and 4th answers only
The 1st, 3rd, and 4th answers only
All of the above

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2 points

Question 4
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If a study fails to detect a significant difference between treatment A and treatment B when in fact
the treatments do differ, the following type of error has occurred.Answer
Type I error
Type II error
Treatment discrimination error
Difference testing error

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2 points

Question 5

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Controls are needed in a case­control study to evaluate whether the frequency of a factor or past
exposure among the cases is different from that among comparable persons who do not have the
disease under investigation.AnswerTrue False

2 points

Question 6
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Controlled clinical trials enable researchers to:Answer
Derive knowledge about the origins of a disease
Control the level of exposure to a treatment
More accurately identify cause and effect
All of the above

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2 points

Question 7
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A case­control study was conducted to identify risk factors for the common cold. Living with
children under the age of 10 was one of the risk factors evaluated. The odds ratio for this association
was 9.0, and the 95% confidence interval ranged from 1.2 to 85. Which of the following statements is
true about this association?Answer

People who lived with a child under the age of 10 had 9 times the risk of getting a cold com
The P value was greater than 0.05.
The P value was less than 0.05.
The association was statistically significant.
The true strength of association could be estimated more precisely if the study were repeat
The 1st and 2nd answers only
The 1st and 3rd answers only
The 1st, 3rd, 4th, and 5th answers only
The 1st, 2nd, and 5th answers only

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2 points

Question 8
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What sources can be used to identify controls for a case­control study?Answer
General population
Hospital/clinic patients
Friends and relatives
All of the above

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2 points

Question 9
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When assessing a positive relationship between alcohol consumption and oral cancer using a case­
control study, increasing the sample size of the study will result in which of the following? Answer
A lower P value
A greater odds ratio

A smaller 95% confidence interval
A higher disease prevalence
The 1st and 3rd answers only
The 2nd and 4th answers only
The 1st, 2nd, and 3rd answers only
All of the above
None of the above

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2 points

Question 10
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A southwestern state passed a law in 1988 making it illegal to drive without wearing a seat belt. To
determine whether the law had made a difference in terms of mortality, a researcher in the state
health department compiled data on deaths due to vehicle crashes in the 5 years before 1988 and in
the 5 years after 1988. What type of study is this?Answer
Randomized controlled trial
Concurrent cohort study
Retrospective cohort study
Case­control study
Nested case­control study
Cross­sectional study
Ecologic study

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2 points

Question 11
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Any systematic error in the design or conduct of a study that results in an incorrect estimate of an
exposure’s effect on the risk of disease is called: Answer
Confounding
Bias
Stratification
Effect modification

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2 points

Question 12
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For a variable to be a confounder, it must be:Answer
Associated with the disease (outcome) under study
Associated with the risk factor (exposure) under study
Both of the above
Neither of the above

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Question 13
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2 points

Which one of the following statements best describes a limitation of cross­sectional studies? Answer

No information on individuals
Unclear temporal relationship between exposure and disease
No comparison group

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2 points

Question 14
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The primary difference between an experimental and observational study is:Answer

The investigator is "blinded" (prevented from knowing the subjects’ true exposure status u
observational study.
The investigator controls the subject’s exposure in an experimental study but not in an obs
The investigator controls the subject’s outcome in an experimental study but not in an obse
Experimental studies are conducted with animals; observational studies are conducted with

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2 points

Question 15
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Over the past 2 years, efforts were made to identify and determine the mortality and morbidity
experience of several thousand military personnel who were stationed in the Persian Gulf and
elsewhere in Europe in 1991. What type of study is this?Answer
Case­control study
Prospective cohort study
Retrospective cohort study
Randomized trial

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2 points

Question 16
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A cross­sectional study of the relationship between blood type and the risk of cataracts will produce
misleading results because you cannot tell the correct temporal relationship between the exposure
(blood type) and disease (cataracts).AnswerTrue False

2 points

Question 17
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Researchers collected baseline information on oral contraceptive use from a group of female college
seniors from a large university. Each year for the next 20 years, the women were followed up on to
determine whether or not the participants had developed any of several conditions. What type of
study is this?Answer
Case­control study
Prospective cohort study
Retrospective cohort study
Randomized trial
Cross­sectional study

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2 points

Question 18
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The healthy worker effect is a form of what type of bias?Answer
Selection bias
Control­selection bias
Interviewer/recording bias
Surveillance, diagnostic, or referral bias

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2 points

Question 19
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When chance, bias, and confounding have been ruled out as alternative explanations for an
association, we may conclude that the association is causal. AnswerTrue False
2 points

Question 20
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Advantages of a case­control design include all the following except:Answer
It is appropriate for studying rare diseases.
It is appropriate for studying rare exposures.
The odds ratio can provide an estimate of the relative risk.
Multiple exposures can be studied.