Population Health Assessment The Use of 2 by 2 Tables
Population Health Assessment
Jan 21, 2016
Population Health Assessment. The Use of 2 by 2 Tables. Health Assessment. Healthy. UnHealthy. Healthy. UH. HOW TO SEPARATE THE TWO SUBPOPULATIONS?. Health Assessment. SURVEYS. SURVEILLANCE. ON-GOING EPIDEMIOLOGIC INTELLIGENCE. GATHERING. USUALLY LONG TERM. SYSTEMATIC and ORGANIZED. - PowerPoint PPT Presentation
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Population Health Assessment
The Use of 2 by 2 Tables
Healthy
UH
Healthy UnHealthy
HOW TO SEPARATE THE TWO SUBPOPULATIONS?
Health AssessmentHealth Assessment
Health AssessmentHealth Assessment
SURVEYS
SURVEILLANCE
ON-GOING EPIDEMIOLOGIC INTELLIGENCE
GATHERINGUSUALLY LONG TERM
SYSTEMATIC and ORGANIZED
Health AssessmentHealth Assessment
Unhealthy
HEALTHY
H
UH
POPULATION SAMPLE
SAMPLING
MUST BE: 1. UNBIASED
2. REPRESENTATIVE
THIS WILL BE THE ONLY WAY TO MAKE INFERENCES
SAMPLING
NON RANDOM.....CONVENIENCE
RANDOM
1. SIMPLE RANDOM
2. STRATIFIED RANDOM
3. STAGE BY STAGE RANDOM
4. SYSTEMATIC RANDOM
SAMPLING
NON RANDOM.....CONVENIENCERANDOM
#1: SAMPLING PROCEDURE
#2: SAMPLE SIZE Determination
WITH THESE TWO CONSIDERATIONS...ONE CAN PROCEED
TO ASSESS THE HEALTH OF A POPULATION UNDER STUDY
Need to Have the Knowledge Base and Skills in:
Healthy
UH
Healthy UnHealthy
HOW TO SEPARATE THE TWO SUBPOPULATIONS?
Health AssessmentHealth Assessment
The Use of TEST SYSTEMS
TEST SYSTEMS
CLINICAL
IMMUNO-DIAGNOSTIC
PHYSIO-CHEMICAL
OTHERS
ONE COMMON CHARACTERISTICS OF TEST SYSTEMS ?
FALLACIES AND INACCURACIES
Health AssessmentHealth Assessment
TEST SYSTEMS
FALLACIES AND INACCURACIESTEST POSITIVES
TEST NEGATIVES
WHAT DOES IT MEAN ? COULD MEAN ?
TEST SYSTEMS
FALLACIES AND INACCURACIES
TEST POSITIVES
TEST NEGATIVES
WHAT DOES IT MEAN ? COULD MEAN ?
HOW TO ASSESS OR ESTIMATE INACCURACIES.....
TEST SYSTEMS
TEST SENSITIVITY AND TEST SPECIFICITY
AND OTHER MEASURES
Se
Sp
F+
F-
PREDICTIVE VALUES (+ or -)
DIAGNOSABILITY
TEST SYSTEMS
TEST
SYSTEM
+
-
TOTALS
Refer to Exercise
Test Negatives
Test Positives
The 2 By 2 Table: How to Create it??
How to Create a 2 By 2 Table???
Why do we need it? Where do we Get the data to insert in these Tables??
TEST SYSTEMS
TEST
SYSTEM
+
-
SUB-TOTALS
SUB-TOTALS
D+ D-
STATE OF NATURE
Note: How to Cross Classify to Create the 2 By 2 Table.
TEST SYSTEMS
TEST
SYSTEM
+
-
SUB-TOTALS
SUB-TOTALS
D+ D-
STATE OF NATURE
a b
c d
a+b
c+d
a+c b+d n=a+b+c+d
Note: How to Cross Classify to Create the 2 By 2 Table
TEST SYSTEMS
TEST
SYSTEM
+
-
SUB-TOTALS
SUB-TOTALS
D+ D-
STATE OF NATURE (Gold Standard)
a b
c d
a+b
c+d
a+c b+d n=a+b+c+d
Se= P(T+/D+)= a/(a+c) Sp= P(T-/D-)= d/(b+d)
TEST SYSTEMS
TEST
SYSTEM
+
-
SUB-TOTALS
SUB-TOTALS
D+ D-
STATE OF NATURE (Gold Standard)
a b
c d
a+b
c+d
a+c b+d n=a+b+c+d
Se= P(T+/D+)= a/(a+c) Sp= P(T-/D-)= d/(b+d)
F+= P(T+/D-)= b/(b+d) F-=P(T-/D+)=c/(a+c)
TEST SYSTEMS
TEST
SYSTEM
+
-
SUB-TOTALS
SUB-TOTALS
D+ D-
STATE OF NATURE (Gold Standard)
a b
c d
a+b
c+d
a+c b+d n=a+b+c+d
Predictive value(+)=a/(a+b)
Predictive value(-)=d/(c+d)
True Prevalence=(a+c)/n
Apparent Prevalence=(a+b)/n
TEST SYSTEMS
TEST
SYSTEM
+
-
SUB-TOTALS
SUB-TOTALS
D+ D-
STATE OF NATURE
a b
c d
a+b
c+d
a+c b+d n=a+b+c+d
DIAGNOSABILITY= P(D+/T+)=(P(D+)*P(T+/D+))/(P(D+)*P(T+/D+))+((P(D-)*P(T+/D-))
LINK
EXERCISE: CASE PROBLEM #1
TEST SYSTEMS EXERCISE Given
True prevalence 38%True prevalenceIHA test positives 250
IHA test positives
IHA positives 260IHA positives Given
True prevalence 38%Infected/diseased 250IHA test positives 260IHA test negatives 478
DATA GIVEN
IHA test - 478 65%IHA test + 260 35%
738 100%
EXERCISE: CASE PROBLEM #1
D+ D- Marginal totalsT+ a b a+b
T- c d c+d
Marginal totals a+c b+d n
True Prev (a+c)/n 280Apparent Hlthy (c+d)/n 478
EXERCISE: CASE PROBLEM #1
TEST SYSTEMS EXERCISE
Option #1 D+
D- Marginal totals
T+ 250 10 260
T- 30 448 478Marginal totals 280 458 738
EXERCISE: CASE PROBLEM #1TEST SYSTEMS EXERCISE
Option #1 D+
D- Marginal totals
T+ 250 10 260
T- 30 448 478
Marginal totals 280 458 738
Se P(T+/D+) a/(a+c) 89.29%
Sp P(T-/D-) d/(b+d) 97.82%
F+ P(T+/D-) b/(b+d) 2.18%
F- P(T-/D+) c/(a+c) 10.71%
EXERCISE: CASE PROBLEM #1
TEST SYSTEMS EXERCISE
D+
D- Marginal totals
T+ 250 10 260T- 30 448 478Marginal totals 280 458 738
Se P(T+/D+) a/(a+c) 89.29%Sp P(T-/D-) d/(b+d) 97.82%
F+ P(T+/D-) b/(b+d) 2.18%F- P(T-/D+) c/(a+c) 10.71%
EXERCISE: CASE PROBLEM #1Note How Data in the Table is Presented
TEST SYSTEMS EXERCISEOption #1
D+
D-
Marginal totals
T+ 250 10 260T- 30 448 478Marginal totals 280 458 738
Se P(T+/D+) a/(a+c) 89.29%Sp P(T-/D-) d/(b+d) 97.82%
F+ P(T+/D-) b/(b+d) 2.18%F- P(T-/D+) c/(a+c) 10.71%
TEST SYSTEMS EXERCISEOption #2
T+
T-
Marginal totals
D+ 250 30 280D- 10 448 458Marginal totals 260 478 738
Se P(T+/D+) 89.29%Sp P(T-/D-) 97.82%
F+ P(T+/D-) 2.18%F- P(T-/D+) 10.71%
EXERCISE: CASE PROBLEM #1Note How Data in the Table is
PresentedTEST SYSTEMS EXERCISE
Option #3
D-
D+
Marginal totals
T+ 10 250 260T- 448 30 478Marginal totals 458 280 738
Se P(T+/D+) 89.29%Sp P(T-/D-) 97.82%
F+ P(T+/D-) 2.18%F- P(T-/D+) 10.71%
TEST SYSTEMS EXERCISEOption #4
T-
T+
Marginal totals
D+ 30 250 280D- 448 10 458Marginal totals 478 260 738
Se P(T+/D+) 89.29%Sp P(T-/D-) 97.82%
F+ P(T+/D-) 2.18%F- P(T-/D+) 10.71%
Bonus QuestionBonus Question
Discuss Diagnosability as a Decision Making Exercise
Good LuckGood Luck
Refer to Online Epidemiology Course @:
http://www.onemedicine.tuskegee.edu
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