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  • 1. At first glance this study might appear to be cross-sectional because a telephone interview was used. However, the data collected pertained to exposures that occurred prior to development of the disease (for the cases). Therefore, this study is best described as case–control.

    2. This is not a classic crossover clinical trial because patients who received the therapy were not subsequently given a placebo. Why would a modified crossover study be necessary in this study?

    3. This study design is interesting, and some might be tempted to call it case–control. The purpose was to compare self-reported therapy with actual therapy. Both of these measures (self-reported and actual) occurred at the same time, so the study also has some characteristics of a cross-sectional study. Our opinion is that the study is case-control, but it illustrates the difficulty in classifying studies cleanly into any scheme.

    4. The study is observational and evaluates the clinical experiences of students who felt competent and those who did not feel competent in performing cancer screening exams. Because the direction of the question is looking back to learn about clinical experiences, the study is a case–control study.

    5. The study is a placebo- (diuretic) controlled randomized clinical trial. In actuality, patients were randomly assigned to different regimens, although we did not provide that information in the description.

    6. The group of subjects was identified and initial data collection occurred in 1976; the same subjects were followed up in future years. The study design is therefore best described as a cohort or prospective study to identify risk factors.

    7. This study collects two kinds of information (physical signs and a laboratory procedure) to compare the diagnostic accuracy of the physical signs. Although there may be a few days between the signs and the result of the lumbar puncture, the research question is the relationship between the two. Therefore, this is a typical case–control study.

    8. This study examines the relationship between risk factors (provider volume) and outcomes in a group of patients undergoing surgery. The research question was clearly forward—what will happen—although the investigators used an existing database. We therefore classify this as a historic cohort study.

    9. The best design is cohort study, which follows a group of subjects over time to see whether lung cancer develops more often in those with a positive screening test; however, this study design would take several years to complete. To avoid the extended time period, these investigators collected data on patients with and without lung cancer and looked back at their screening test results. Because the direction of the question is backward, the study would be best called case–control.

    10. Several study designs are possible, but the most realistic is an observational study. A case–control study provides information faster, but several case–control studies are required; a group of cases for each cause of death and type of cardiovascular morbidity needs to be identified. We suggest you use one of the electronic search programs to see if you ...

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