unit 12 pt 2 - Unit 12 Screening in Epidemiology (part 2)...

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Unit 12 Screening in Epidemiology (part 2 (part 2) Screening and evaluation of diagnostic tools Dr. A. Sanchez-Anguiano Epidemiology 6000 NO AUDIO ON THIS SLIDE Reliability of Screening Tests Reliability (also known as precision) : --The extent to which the screening test will produce the same or very similar results each time it is administered • A test must be reliable before it can be valid (an invalid test can demonstrate high reliability: the answer is wrong each time) Reliability of Screening Tests Sources of variability that can affect the reproducibility of results of a screening test: 1. Biological variation (e.g. blood pressure, cholesterol) 2 Reliability of the instrument itsel 2. Reliability of the instrument itself 3. Intra-observer variability (differences in repeated measurement by the same screener measurement by the same screener) 4. Inter-observer variability (inconsistency in the way different screeners apply or interpret test results different screeners apply or interpret test results) Measuring the Performance (Yield) of a Test ± The proportion of persons who screen positive on the test who actually have Disease ± Predictive Value Positive (PV+ or PPV) ± The proportion of persons who screen negative on the test who are actually free of the Disease Predictive Value Negative (PV or NPV ± Predictive Value Negative (PV- or NPV) Performance (Yield) True Disease Status + - a b Results of + a + b d c screening test - c + d Positive predictive value (PPV): Among persons who test positive the probability that a person actually has the
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This note was uploaded on 07/15/2011 for the course PHC 6000 taught by Professor Staff during the Summer '08 term at University of South Florida - Tampa.

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unit 12 pt 2 - Unit 12 Screening in Epidemiology (part 2)...

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