lecture 10

# lecture 10 - Evaluating Disease Lecture 10 2 X 2 Tables o...

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1 Lecture 10 2 X 2 Tables Evaluating Disease o Epi studies aim to o Evaluate the exposure-disease relationship o Extrapolate study findings to larger populations o To assess the association between exposure and disease, we must compare two groups o Exposed vs. Unexposed o Disease vs. No Disease 2x2 Contingency Tables Total Exposure Status a +b + c + d b + d a + c c + d d c No a + b b a Yes Total No Yes Disease Status Epi studies usually organize data in tables o Disease status goes in columns o Exposure status goes in rows What does the 2x2 table tell us? o Total number of people in the study o Number of people who have the outcome and number who don’t have the outcome o Number of people who are exposed and number who are unexposed o Allows us to calculate measures of association o Relative Risk o Odds Ratio o Attributable Risk o Attributable Risk Percent Relative Risk o Measure of association for a cohort study o Describes risk of developing disease in the exposed group as compared to those who were unexposed o RR = 1.0 means that the risk in the exposed is equal to the risk in the unexposed Relative Risk o RR = 1.0 o Risk of disease is the same for both exposed and unexposed o Exposure is not a risk factor for disease o RR > 1.0 o Increased risk of disease in exposed o Exposure is a risk factor for disease o RR < 1.0 o Decreased risk of disease in exposed o Exposure is protective for disease

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2 Calculating Relative Risk RR = incidence in exposed or I e = incidence in unexposed or I n RR = a / (a + b) c / (c + d) RR = 25 / (25 + 120) 34 / (34 + 276) Total Exposure Status 455 396 59 310 276 34 No 145 120 25 Yes Total No Yes Disease Status 25 / 145 = 1.57 What does this mean? = 34 / 310 Interpreting the RR RR = 1.57 Interpretation: People who are exposed are 1.57 times as likely to develop disease compared to those who are not exposed Odds Ratio o Measure of association for a case- control study o Describes likelihood of diseased people having the exposure relative to those who do not have the disease o Estimates the Relative Risk o The OR is an estimate because we can’t calculate incidence in case-control studies Odds Ratio o OR = 1.0 o No difference in exposure between cases and controls o Disease is not associated with exposure
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## This note was uploaded on 04/06/2008 for the course PUBLIC HEA 832:335 taught by Professor Schneider during the Spring '08 term at Rutgers.

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lecture 10 - Evaluating Disease Lecture 10 2 X 2 Tables o...

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