IN The Use of 2 by 2 Tables CAUSAL ASSOCIATIONS. Causality ASSOCIATION BETWEEN FACTOR AND HEALTH...
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IN The Use of 2 by 2 Tables CAUSAL ASSOCIATIONS
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Transcript of IN The Use of 2 by 2 Tables CAUSAL ASSOCIATIONS. Causality ASSOCIATION BETWEEN FACTOR AND HEALTH...
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 COHORTPROSPECTIVE OR COHORT
F+
F-
D+
D-
TIME
Epidemiologic Methods
F+
F-
D+
D-
TIME
RETROSPECTIVE OR CASE-CONTROLRETROSPECTIVE OR CASE-CONTROL
Epidemiologic Methods
RISK ANALYSIS
THE USE OF THE 2X2 TABLE
D+ D- Total IR
F+
F-
Tot
a b
c d
a+b
c+d
a+c b+d n
a/(a+b)
c/(c+d)
(a+c)/n
AR RR
AR= (a/(a+b)-(c/(c+d)))RR= (a/(a+b))/(c/(c+d)))
Epidemiologic MethodsRISK ANALYSIS
THE USE OF THE 2X2 TABLE
D+ D- Total IR
F+
F-
Tot
a b
c d
a+b
c+d
a+c b+d n
a/(a+b)
c/(c+d)
(a+c)/n
RR(exact)= (a/(a+b))/(c/(c+d)))
(PROSPECTIVE or COHORT)
EXERCISE: CASE ProblemEXERCISE: CASE Problem #2 #2
Calf Mortality Exercise
Given
300 calves born in corrals No. dead 100
90 calves born in barn No. dead 9
Crude mortality rate CMR0.33333333
3 33.3%
(corrals)
Crude mortality rate Barn 0.1 10.0%
EXERCISE: CASE Problem #2EXERCISE: CASE Problem #2
2 X 2 Table Prospective design
D+
D-
total
Incidence rate (IR)
Corral 100 200 300 33.3%
Barn 9 81 90 10.0%
109 281 390
Relative Risk (exact) Rre 3.333333333
Attributable Risk AR 0.233333333 23.30%
Epidemiologic Methods
F+
F-
D+
D-
TIME
RETROSPECTIVE OR CASE-CONTROLRETROSPECTIVE OR CASE-CONTROL
Epidemiologic MethodsRISK ANALYSIS
THE USE OF THE 2X2 TABLE
D+ D- Total IR
F+
F-
Tot
a b
c d
a+b
c+d
a+c b+d n
RR(approx)= Odds Ratio=(a*d/c*b)
(RETROSPECTIVE or CASE CONTROL)
UNKNOWN
EXERCISE: CASE Problem #2EXERCISE: CASE Problem #2
2 X 2 Table Retrospective design D+
D-
total
Corral 100 200 300Barn 9 81 90
109 281 390
Odds Ratio OR 4.5
Causality
F+ D+
STATISTICAL ASSOCIATION
SA
USE OF THE CHI SQUARE
Causality
STATISTICAL ASSOCIATION
THE 2 by 2 TABLE.
D+ D-
F+
F-
a b
c d
a+b
c+da+c b+d n
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 OutbreakFood-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-
a b
c d
a+b
c+da+c b+d n
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
