IN The Use of 2 by 2 Tables CAUSAL ASSOCIATIONS

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

Causality ASSOCIATION APPARENT STATISTICAL CAUSAL

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

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

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)))

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)

EXERCISE: CASE Problem #2 Calf Mortality Exercise Given 300 calves born in corralsNo. dead calves born in barnNo. dead9 Crude mortality rateCMR % (corrals) Crude mortality rateBarn %

EXERCISE: CASE Problem #2 2 X 2 TableProspective design D+ D- total Incidence rate (IR) Corral % Barn % Relative Risk (exact)Rre Attributable RiskAR %

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

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

EXERCISE: CASE Problem #2 2 X 2 TableRetrospective design D+ D- total Corral Barn Odds RatioOR4.5

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

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

IN The Use of 2 by 2 Tables OUTBREAK INVESTIGATIONS

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

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

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