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#1
08-05-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,867 Threads: 149 Thanked 2,089 Times in 1,047 Posts Reputation: 2109
What type of study

A group of patients with lung cancer is matched to a group of patients without lung cancer. Their smoking habits
over the course of their lives is compared. Based on this information, researchers compute the rate of lung
cancer in patients who smoke versus those who never smoked. This is an example of a

A. case-control study

B. cohort study

C. cross-sectional study

D. longitudinal study

E. randomized controlled study

#2
08-05-2012
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 730 Threads: 90 Thanked 456 Times in 289 Posts Reputation: 466

A....................
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#3
08-05-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,867 Threads: 149 Thanked 2,089 Times in 1,047 Posts Reputation: 2109

Explanation:

The correct answer is A. Case-control studies are retrospective and are as described in the question stem.
Case-control studies allow researchers to compute an odds ratio.

In cohort studies (choice B), subjects are assembled on the basis of some common experience (such as
attending medical school) and are then monitored for a specified amount of time at regular intervals (e.g.,
taking USMLE Steps 1, 2, and 3; see also longitudinal studies below) until they develop the outcome of interest
(they become practicing physicians) or the follow-up time ends. The cohort study minimizes many of the biases
evident in case-control designs and is the definitive observational clinical study. Cohort studies allow
researchers to compute a relative risk.

Cross-sectional studies (choice C) usually have more modest goals than those of case-control and cohort
studies. A variable or group of variables is measured in a sample of a larger population to get an idea of the
distribution and interrelationships of those variables in that population.

Longitudinal studies (choice D) identify individual subjects and follow them over a given period of time. For
example, the study of cholesterol-lowering drugs on cardiovascular events requires that the same subject is
observed over a significant period of time (e.g., 10 years).

A randomized controlled trial (choice E) is considered the most rigorous and powerful approach to answering a
clinical question in which two treatments, strategies, or therapies are compared or when one therapy is
compared to placebo. In this type of study, subjects are assigned treatments on a randomized basis.
 The above post was thanked by: chriledi (04-08-2013)

 Tags Biostatistics-Epidemiology, Step-2-Questions

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