Question

A group of pregnant women were followed prospectively to investigate the role of cigarette smoking and risk of low birth weight. At the first prenatal visit, 2200 women were classified as current smokers or non-smokers (defined as former smokers or never smokers). The outcome, low birthweight, was defined as a birthweight < 2500 grams. After completion of the study, the investigators reported the results in the form of calculated rates and measures of effect. What study design was used to by these investigators to evaluate the association between smoking and LBW? The following data were obtained: Smokers <2500 345 114 Birthweight >= 2500 252 1489 1741 Non-Smokers 597 1603 2200 459 1. What is the cumulative incidence of low birth weight (LBW) among the "exposed" women? 2. What is the cumulative incidence of LBW among the unexposed women? 3. What is the incidence of LBW among all women in the study? 4. What is the relative risk of having a LBW baby for a smoker vs. a non-smoker?

Answer 1

Formulas: DCumulative incidence Total no of ina for a specihic Hime intrval No.of new events of dislase in the populahion at risk (exposed women 345 -0.15687 22 00 0518 l14 unex posed women 2200 incidence rate Total no of new cases of a Apecilte disease durfng Hme period Tatal papulation at risk during the same time peniod 459 2200 a givea Xlare 208.636

( Relative risk Probability of an event occuning gzoups Probability of an event occurin4 tor 3.026 345 I14 Relative risk