Create Presentation
Download Presentation

Download Presentation
## The Use of 2 by 2 Tables

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**The Use of 2 by 2 Tables**IN CAUSAL ASSOCIATIONS**Causality**ASSOCIATION BETWEEN FACTOR AND HEALTH EVENT ??? F+ D+**Causality**APPARENT ASSOCIATION STATISTICAL CAUSAL**Epidemiologic Methods**PROSPECTIVE OR COHORT TIME F+ D+ F- D-**Epidemiologic Methods**TIME F+ D+ F- D- RETROSPECTIVE OR CASE-CONTROL**Epidemiologic Methods**RISK ANALYSIS THE USE OF THE 2X2 TABLE D+ D- Total IR AR RR a+b F+ a b a/(a+b) F- c d c+d c/(c+d) Tot a+c b+d n (a+c)/n AR= (a/(a+b)-(c/(c+d))) RR= (a/(a+b))/(c/(c+d)))**Epidemiologic Methods**RISK ANALYSIS (PROSPECTIVE or COHORT) THE USE OF THE 2X2 TABLE D+ D- Total IR a+b F+ a b a/(a+b) F- c d c+d c/(c+d) Tot a+c b+d n (a+c)/n RR(exact)= (a/(a+b))/(c/(c+d)))**Epidemiologic Methods**TIME F+ D+ F- D- RETROSPECTIVE OR CASE-CONTROL**Epidemiologic Methods**RISK ANALYSIS THE USE OF THE 2X2 TABLE (RETROSPECTIVE or CASE CONTROL) D+ D- Total IR a+b F+ a b UNKNOWN F- c d c+d Tot a+c b+d n RR(approx)= Odds Ratio=(a*d/c*b)**Causality**STATISTICAL ASSOCIATION USE OF THE CHI SQUARE SA F+ D+**Causality**THE 2 by 2 TABLE. STATISTICAL ASSOCIATION Disease Outcome D+ D- NULL HYPOTHESIS F+ a b a+b ALTERNATE HYPOTHESIS Exposure to Risk F- c d c+d Level of sig (a=0.05) a+c b+d n df for 2X2= 1 FOR DECISION Compare ChiSquare calculated ChiSq= (ad-bc)**2n To ChiSquare tabulated (3.84) (a+c)(a+b)(b+d)(c+d)**The Use of 2 by 2 Tables**IN OUTBREAK INVESTIGATIONS**Causality**ASSOCIATION BETWEEN Food Eaten & Disease (outcome) ??? F+ D+**Epidemiologic Methods**Food-Borne Outbreak F+ D+ Eaten Risky Food Outcome Disease F- Not Eat Risky Food D- OUTCOME NO DISEASE**Causality**THE 2 by 2 TABLE. STATISTICAL ASSOCIATION Disease Outcome D+ D- NULL HYPOTHESIS F+ a b a+b ALTERNATE HYPOTHESIS Exposure to Risk F- c d c+d Level of sig (a=0.05) a+c b+d n df for 2X2= 1 FOR DECISION Compare ChiSquare calculated ChiSq= (ad-bc)**2n To ChiSquare tabulated (3.84) (a+c)(a+b)(b+d)(c+d)