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CHP400: Community Health Program-lI Mohamed M. B. Alnoor Muna M H Diab SCREENING.

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Presentation on theme: "CHP400: Community Health Program-lI Mohamed M. B. Alnoor Muna M H Diab SCREENING."— Presentation transcript:

1 CHP400: Community Health Program-lI Mohamed M. B. Alnoor Muna M H Diab SCREENING

2 Suitable Screening Test : Acceptable Safe Rapid Inexpensive Easy to do Valid Reliable Valid Reliable

3 SCREENING Suitable Screening Test : Acceptable Safe Rapid Inexpensive Easy to do Validity: (Sensitivity, Specificity) Reliability: (repeatability/precision) Yield (performance): Predictive values of the test.

4 SCREENING Validity of Screening Test : How good is the screening test compared with the confirmatory diagnostic test (Gold Standard test)? The test will correctly classify a diseased person as likely to have the condition (“sensitivity”). The test will correctly classify a non- diseased person as unlikely to have the condition (“specificity”).

5 SCREENING Validity of Screening Test : Total Gold standard Screening test NegativePositive PS(FP)(TP) Positive NS(TN)(FN) Negative GTTHTD Total Screening test compared to gold standard a b c d

6 SCREENING Validity of Screening Test : a d c b True Disease Status + - Results of Screening Test + - Sensitivity: The probability of testing positive if the disease is truly present Sensitivity = a / (a + c)

7 SCREENING Validity of Screening Test : a d c b True Disease Status Specificity: The probability of screening negative if the disease is truly absent Specificity = d / (b + d) Results of Screening Test

8 SCREENING Adverse effects of screening: Stress and anxiety caused by a false positive screening results. Unnecessary investigation and treatment of false positive results Prolonging knowledge of an illness if nothing can be done about it. A false sense of security caused by false negatives, which may delay final diagnosis. Overuse/waste of medical resources.

9 SCREENING Validity of Screening Test : Disease Test DNo D Sensitivity: a / (a + c) = 90/100 =90% Specificity: d / (b + d) = 95/100 =95% Prevalence of disease =(a+c)/(a+b+c+d) =100/200 =50% a b c d

10 SCREENING Reliability of Screening Test : RELIABILITY (Reproducibility) Precision: The extent to which the screening test will produce the same (or very similar) results each time it is administered (repeated). --- A test must be reliable before it can be valid.

11 SCREENING Yield(Performance) of Screening Test: Yield is the amount of previously unrecognized disease that is diagnosed and brought to treatment as a result of screening. It is measured by: Predictive Value Positive (PV+) Predictive Value Positive (PV+) Predictive Value Negative (PV-) Predictive Value Negative (PV-)

12 SCREENING Yield(Performance) of Screening Test: a d c b True Disease Status + - Results of Screening Test + - Predictive value positive (PV+): The probability that a person actually has the disease given that he or she tests positive. i.e. The ability to predict the presence of disease from test results. PV+ = a / (a + b)

13 SCREENING Yield(Performance) of Screening Test: a d c b True Disease Status + - Results of Screening Test + - Predictive value negative (PV-): The probability that a person is truly disease free given that he or she tests negative. i.e. The ability to predict the absence of disease from test results. PV- = d / (c + d)

14 SCREENING Yield(Performance) of Screening Test: Disease Test DNo D a b c d Calculate: PV+ =19/118=16% PV-= 1881/1882=99.95%

15 SCREENING Yield(Performance) of Screening Test: Disease Test DNo D a b c d Calculate: PV+ =57/59=96.6% PV-= 38/41=93%

16 SCREENING Factors affecting Yield : Prevalence (%) Sensitivity Specificity PV % 95% 15.4% 2.090% 95% 26.7% 9.090% 95% 64.5% % 95% 94.8%

17 SCREENING Validity &Reliability of Screening Test :

18 SCREENING Validity &Reliability of Screening Test :


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