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
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 ...