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IN The Use of 2 by 2 Tables CAUSAL ASSOCIATIONS

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Causality ASSOCIATION BETWEEN FACTOR AND HEALTH EVENT F+D+ ???

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Causality ASSOCIATION APPARENT STATISTICAL CAUSAL

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Epidemiologic Methods PROSPECTIVE OR COHORT F+ F- D+ D- TIME

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Epidemiologic Methods F+ F- D+ D- TIME RETROSPECTIVE OR CASE-CONTROL

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Epidemiologic Methods RISK ANALYSIS THE USE OF THE 2X2 TABLE D+D-TotalIR F+ F- Tot ab cd a+b c+d a+cb+dn a/(a+b) c/(c+d) (a+c)/n ARRR AR= (a/(a+b)-(c/(c+d))) RR= (a/(a+b))/(c/(c+d)))

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Epidemiologic Methods RISK ANALYSIS THE USE OF THE 2X2 TABLE D+D-TotalIR F+ F- Tot ab cd a+b c+d a+cb+dn a/(a+b) c/(c+d) (a+c)/n RR(exact)= (a/(a+b))/(c/(c+d))) (PROSPECTIVE or COHORT)

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EXERCISE: CASE Problem #2 Calf Mortality Exercise Given 300 calves born in corralsNo. dead100 90 calves born in barnNo. dead9 Crude mortality rateCMR0.33333333333.3% (corrals) Crude mortality rateBarn0.110.0%

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EXERCISE: CASE Problem #2 2 X 2 TableProspective design D+ D- total Incidence rate (IR) Corral10020030033.3% Barn9819010.0% 109281390 Relative Risk (exact)Rre3.333333333 Attributable RiskAR0.23333333323.30%

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Epidemiologic Methods F+ F- D+ D- TIME RETROSPECTIVE OR CASE-CONTROL

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Epidemiologic Methods RISK ANALYSIS THE USE OF THE 2X2 TABLE D+D-TotalIR F+ F- Tot ab cd a+b c+d a+cb+dn RR(approx)= Odds Ratio=(a*d/c*b) (RETROSPECTIVE or CASE CONTROL) UNKNOWN

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EXERCISE: CASE Problem #2 2 X 2 TableRetrospective design D+ D- total Corral100200300 Barn98190 109281390 Odds RatioOR4.5

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Causality F+D+ STATISTICAL ASSOCIATION SA USE OF THE CHI SQUARE

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Causality STATISTICAL ASSOCIATION THE 2 by 2 TABLE. D+D- F+ F- ab cd a+b c+d a+c b+dn ChiSq= (ad-bc)**2n (a+c)(a+b)(b+d)(c+d) NULL HYPOTHESIS ALTERNATE HYPOTHESIS Level of sig (a=0.05) df for 2X2= 1 FOR DECISION Compare ChiSquare calculated To ChiSquare tabulated (3.84) Exposure to Risk Disease Outcome

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IN The Use of 2 by 2 Tables OUTBREAK INVESTIGATIONS

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Causality ASSOCIATION BETWEEN Food Eaten & Disease (outcome) F+D+ ???

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Epidemiologic Methods Food-Borne Outbreak F+ F- D+ D- Eaten Risky Food Not Eat Risky Food Outcome Disease OUTCOME NO DISEASE

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Causality STATISTICAL ASSOCIATION THE 2 by 2 TABLE. D+D- F+ F- ab cd a+b c+d a+c b+dn ChiSq= (ad-bc)**2n (a+c)(a+b)(b+d)(c+d) NULL HYPOTHESIS ALTERNATE HYPOTHESIS Level of sig (a=0.05) df for 2X2= 1 FOR DECISION Compare ChiSquare calculated To ChiSquare tabulated (3.84) Exposure to Risk Disease Outcome

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