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Population Health Assessment The Use of 2 by 2 Tables.

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Presentation on theme: "Population Health Assessment The Use of 2 by 2 Tables."— Presentation transcript:

1 Population Health Assessment The Use of 2 by 2 Tables

2 Healthy UH Healthy UnHealthy HOW TO SEPARATE THE TWO SUBPOPULATIONS? Health Assessment

3 SURVEYS SURVEILLANCE ON-GOING EPIDEMIOLOGIC INTELLIGENCE GATHERING USUALLY LONG TERM SYSTEMATIC and ORGANIZED

4 Health Assessment Unhealthy HEALTHY H UH POPULATIONSAMPLE

5 SAMPLING MUST BE: 1. UNBIASED 2. REPRESENTATIVE THIS WILL BE THE ONLY WAY TO MAKE INFERENCES

6 SAMPLING NON RANDOM.....CONVENIENCE RANDOM 1. SIMPLE RANDOM 2. STRATIFIED RANDOM 3. STAGE BY STAGE RANDOM 4. SYSTEMATIC RANDOM

7 SAMPLING NON RANDOM.....CONVENIENCE RANDOM #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:

8 Healthy UH Healthy UnHealthy HOW TO SEPARATE THE TWO SUBPOPULATIONS? Health Assessment The Use of TEST SYSTEMS

9 TEST SYSTEMS CLINICAL IMMUNO-DIAGNOSTIC PHYSIO-CHEMICAL OTHERS ONE COMMON CHARACTERISTICS OF TEST SYSTEMS ? FALLACIES AND INACCURACIES Health Assessment

10 TEST SYSTEMS FALLACIES AND INACCURACIES TEST POSITIVES TEST NEGATIVES WHAT DOES IT MEAN ? COULD MEAN ?

11 TEST SYSTEMS FALLACIES AND INACCURACIES TEST POSITIVES TEST NEGATIVES WHAT DOES IT MEAN ? COULD MEAN ? HOW TO ASSESS OR ESTIMATE INACCURACIES.....

12 TEST SYSTEMS TEST SENSITIVITY AND TEST SPECIFICITY AND OTHER MEASURES Se Sp F+ F- PREDICTIVE VALUES (+ or -) DIAGNOSABILITY

13 TEST SYSTEMS TEST SYSTEM + - TOTALS Refer to Exercise Test Negatives Test Positives

14 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??

15 TEST SYSTEMS TEST SYSTEM + - SUB-TOTALS D+D- STATE OF NATURE Note: How to Cross Classify to Create the 2 By 2 Table.

16 TEST SYSTEMS TEST SYSTEM + - SUB-TOTALS D+D- STATE OF NATURE ab cd 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

17 TEST SYSTEMS TEST SYSTEM + - SUB-TOTALS D+D- STATE OF NATURE (Gold Standard) ab cd 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)

18 TEST SYSTEMS TEST SYSTEM + - SUB-TOTALS D+D- STATE OF NATURE (Gold Standard) ab cd 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)

19 TEST SYSTEMS TEST SYSTEM + - SUB-TOTALS D+D- STATE OF NATURE (Gold Standard) ab cd 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

20 TEST SYSTEMS TEST SYSTEM + - SUB-TOTALS D+D- STATE OF NATURE ab cd 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

21 EXERCISE: CASE PROBLEM #1 TEST SYSTEMS EXERCISE Given True prevalence38%True prevalence IHA test positives250IHA test positives IHA positives260IHA positives Given True prevalence38% Infected/diseased250 IHA test positives260 IHA test negatives478 DATA GIVEN IHA test % IHA test % %

22 EXERCISE: CASE PROBLEM #1 D+D-Marginal totals T+ aba+b T- cdc+d Marginal totals a+cb+dn True Prev(a+c)/n280 Apparent Hlthy(c+d)/n478

23 EXERCISE: CASE PROBLEM #1 TEST SYSTEMS EXERCISE Option #1 D+ D-Marginal totals T T Marginal totals

24 EXERCISE: CASE PROBLEM #1 TEST SYSTEMS EXERCISE Option #1 D+ D-Marginal totals T T Marginal totals SeP(T+/D+)a/(a+c)89.29% SpP(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%

25 EXERCISE: CASE PROBLEM #1 TEST SYSTEMS EXERCISE D+ D-Marginal totals T T Marginal totals SeP(T+/D+)a/(a+c)89.29% SpP(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%

26 EXERCISE: CASE PROBLEM #1 Note How Data in the Table is Presented TEST SYSTEMS EXERCISE Option #1 D+ D- Marginal totals T T Marginal totals SeP(T+/D+)a/(a+c)89.29% SpP(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 EXERCISE Option #2 T+ T- Marginal totals D D Marginal totals SeP(T+/D+)89.29% SpP(T-/D-)97.82% F+P(T+/D-)2.18% F-P(T-/D+)10.71%

27 EXERCISE: CASE PROBLEM #1 Note How Data in the Table is Presented TEST SYSTEMS EXERCISE Option #3 D- D+ Marginal totals T T Marginal totals SeP(T+/D+)89.29% SpP(T-/D-)97.82% F+P(T+/D-)2.18% F-P(T-/D+)10.71% TEST SYSTEMS EXERCISE Option #4 T- T+ Marginal totals D D Marginal totals SeP(T+/D+)89.29% SpP(T-/D-)97.82% F+P(T+/D-)2.18% F-P(T-/D+)10.71%

28 Bonus Question Discuss Diagnosability as a Decision Making Exercise

29 Good Luck Refer to Online Epidemiology


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