Epidemiology Lecture 8-2x2Tables – Flashcards
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what does a 2x2 table allow us to calculate?
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relative risk; odds ratio; attributable risk; attributable risk percent
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measure of association for cohort study
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relative risk
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relative risk
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describes risk of developing disease in the exposed group as compared to those who were unexposed
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relative risk RR=1.0
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risk in exposed = risk in unexposed; exposure is not a risk factor for disease
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relative risk RR>1.0
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increased risk of disease in exposed; exposure is a risk factor for disease
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relative risk RR<1.0
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decreased risk of disease in exposed; exposure is a protective factor for disease
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calculate relative risk
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Ie/Iu= incidence_exposed/incidence_unexposed; (a/(a+b))/(c/(c+d))
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relative risk interpretation
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people who are (exposed) are x times as likely to develop (disease) compared to those who are (not exposed)
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measure of association for case-control study
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odds ratio
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odds ratio
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describes likelihood of diseased people having the exposure relative to those who do not have the disease; estimate bc cant calc incidence in c-c
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odds ratio OR=1.0
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no diff in exposure btwn case & control; disease not associated with exposure
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odds ratio OR>1.0
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increased risk of exposure in cases; disease is positively associated with exposure
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odds ratio OR<1.0
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decreased risk of exposure in cases; exposure is protective for disease
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calculate odds ratio
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(a/c)/(b/d) = (ad)/(bc)
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RR~=OR
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when disease is rare
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odds ratio interpretation
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people with the (disease) are (x) times as likely to have been (exposed) relative to those who (do not have the disease)
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how do we compare burden of disease w/in 2 groups?
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attributable risk; attributable risk%; pop attributable risk; pop attributable risk %
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attributable risk/risk difference
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measure of assoc for cohort study; describes excess risk of disease assoc w/ exposure/measures impact
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measures of impact
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provide info about publichealth impact of exposure; contribution of exposure to frequency of disease
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attributable risk
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quantifies disease burden in exposed group attributable to exposure
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calculate attributable risk
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AR = Ie-Iu = a/(a+b)-c/(c+d)
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attributable risk interpretation
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the excess risk of (disease) attributable to (exposure) is (x) per 100 (exposed group)
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attributable risk %
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AR as percent of risk in exposed pop; proportion of disease among exposed which can be attributedto/could be prevented by elim exposure
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calculate attributable risk %
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AR/(a/(a+b))*100 = AR/Ie*100
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attributable risk % interpretation
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(x%) of the (disease) among (exposed group) could be eliminated if we eliminate (exposure)
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AR and AR% in case-control
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not possible now; if OR approx then AR%= (OR-1)/OR *100
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pop attributable risk
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meas for cohort; risk of disease attributable to exposure in total study pop
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calculate pop attributable risk
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Itotalpop - Iu = (a+c)/(a+b+c+d) - c/(c+d)
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pop attributable risk interpretation
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the excess risk of (disease) in the total study pop due to (exposure) is (x) per 100 people; (x) of 100 of (disease) is attributable to (exposure)
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pop attributable risk %
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meas for cohort; describes prop of disease that could be prevented in entire pop if exposure eliminated in entire pop
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calculate pop attributable risk %
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(Ipop-Iu)/(Ipop)*100; PAR/(Itot)*100; PAR/((a+c)/(a+b+c+d))*100
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pop attributable risk % interpretation
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(x%) of the (disease) could be eliminated in the entire study pop if no one in the pop (exposure)
