Multiple Choice Answers


1. Which of the following is a method for controlling confounding in the analysis phase only of a study?

2. A retrospective cohort study compared to a prospective cohort study of the same kind of exposure can be completed more quickly.

3. A cohort study was conducted to examine cigarette smoking and the risk of oral cancer. The investigators selected exposed and unexposed subjects so that they had exactly the same distribution of race. This method to address confounding by race is called:
Multivariate analysis
None of the above

4. 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?
Randomized controlled trial
Concurrent cohort study
Retrospective cohort study
Case-control study
Nested case-control study
Cross-sectional study
Ecologic study

5.Subjects were children enrolled in a health maintenance organization. At 18 months of age, each child was randomly given one of two types of vaccine against Haemophilus influenzae. Parents were asked to record any side effects on a card and mail it back after 2 weeks. What type of study is this?
Case-control study
Concurrent cohort study
Nonconcurrent cohort study
Randomized trial
Cross-sectional study

6. A clinical trial entails comparing a group of patients treated with a test treatment to a comparable group of patients receiving a control treatment.

7.Which of the following will not help to increase study precision (reduce random error)?
Using an accurate measuring instrument
Using an efficient study design
Using a small sample
Using repeat measures

8.In general, a cohort study is preferable to a case-control study in each of the following situations except:
When the exposure is rare
When there are multiple outcomes to be assessed
When the outcome is rare
When recall bias must be minimized

9. Randomized clinical trials can be used for each of the following except:
Evaluation of new drugs
Evaluation of alternate treatments
Assessment of screening programs
Identification of risk factors for disease

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

11.Controls are needed in a case-control 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.

12. Investigators began a study in 1995 to evaluate the association between infertility treatment and ovarian cancer occurrence among 3,000 Rhode Island women treated for infertility between 1984 and 1994. Cancer incidence was determined by matching the women to information in the Rhode Island Cancer Registry. The cancer rates in this sample were compared with cancer rates among the population of Rhode Island women. What kind of t study is this?
Retrospective cohort
Prospective cohort

13.The primary difference between an experimental and observational study is:
The investigator is “blinded” (prevented from knowing the subjects’ true exposure status until the end of the study) in an experimental study but not in an observational study.
The investigator controls the subject’s exposure in an experimental study but not in an observational study.
The investigator controls the subject’s outcome in an experimental study but not in an observational study.
Experimental studies are conducted with animals; observational studies are conducted with humans.

14.In January 1998, a physician in a Buenos Aires, Argentina, hospital telephoned the Ministry of Health (MOH) to report three possible cases of botulism. The patients, all men in their 30s, presented with drooping eyelids, double vision, difficulty swallowing, and respiratory problems. One patient had onset of symptoms on February 2, the other two on February 5. All three men worked in a local meat factory. What type of study is this?
Case report
Case series
Ecological study
Cross-sectional study

15.Which one of the following statements best describes a limitation of cross-sectional studies?
No information on individuals
Unclear temporal relationship between exposure and disease
No comparison group

16. A cross-sectional study allows the demonstration of a time sequence between the exposure and the outcome.

17. Major potential biases in a cohort study can result from each of the following except:
Loss to follow-up
Assessment of outcome

18.A study design method to control confounding involving the selection of study subjects so  that potential confounders are distributed identically is called:
Multivariate modeling

19. Loss-to-follow-up can be a problem in observational studies but not experimental ones.

20. Advantages of a case-control design include all the following except:
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.