Page 1 of 1: incidence-statistic

doctorkarim · Credits: 95917 My Scrapbook

A random selection of 100 female medical students agree to participate in a study of the possible effects of the contraceptive pill. They are followed prospectively for a period of six years to see if there is an association between the incidence of ovarian cysts (demonstrated by ultrasound) and the use of the pill.As the length of survival from HIV AIDS increases because of the new treatment (assuming the rate of new cases diagnosed remains unchanged), the number of cases present at any point in time (prevalence) increases. Incidence, based on the number of new cases only, remains unchanged[color=blue]
How can this study be best described?

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A. Case-control study.
B. Randomised controlled clinical trial.
C. Cross-sectional study.
D. Cohort study.
E. Cross-over study.
answer D
In a case-control study cases (those with the problem) are compared with controls (those without the problem) with regard to the incidence of a specific risk factor (such as use of the pill).
In a randomised controlled clinical trial some members of a cohort with a particular condition are given one treatment while others receive a different (often 'standard') treatment or placebo
NOTE answer taken from refrence book

jabby · Credits: 3703 Preparing for: USMLE Step 2 CK My Scrapbook

cohort study is prospective study in which exposed gr to risk factor is followed over time and compere e other group not exposed to risk factor.outcome is disease incedence in each gr ,prospective subjects tracked in forward time.
must follow population longe enough for incidence to appear.
so i think cohort study describes incidence better.

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