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1. Identify the type of study design. Choose
the best match.
A researcher is investigating a hypothesized association between viral
hepatitis B and carcinoma of the liver. She follows 500 patients with
hepatitis B and 500 patients without hepatitis B for 10 years from the
date of diagnosis of the hepatitis B. She assesses the subsequent frequency
of cancer of the liver among those with and those without hepatitis B.
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Case-Control Study
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Cohort
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Randomized Clinical Trial
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None of the above
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The study and control groups with and without hepatitis B were identified before the outcome, carcinoma of the liver, had occurred or was assessed. In cohort studies the study and control groups are identified prior to assessing the occurrence of the outcome. This distinguishes cohort studies from case-control studies. In a case-control study the investigation would begin by identifying cases with carcinoma of the liver and similar controls without carcinoma of the liver.
Cohort studies are distinguished from randomized clinical trials
by the method of assignment of individuals to study and control
groups. In randomized clinical trials individuals are randomized
to study or control groups. In cohort studies like this one, individuals
are eligible for study and control groups based on their characteristics
or conditions, that is the presence or absence of hepatitis B.
