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Principles of diagnostic sampling – the “ bead game”

Principles of diagnostic sampling – the “ bead game”. Pilot training school in PRRS diagnostics , 2012 Zagreb, Croatia. Dr. Derald Holtkamp September 25, 2012. Exercises. Detecting one or more positive pigs in an expected NEGATIVE population Role of sample size and target prevalence

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Principles of diagnostic sampling – the “ bead game”

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  1. Principles of diagnostic sampling – the “ bead game” Pilot training school in PRRS diagnostics, 2012 Zagreb, Croatia Dr. Derald Holtkamp September 25, 2012

  2. Exercises • Detecting one or more positive pigs in an expected NEGATIVE population • Role of sample size and target prevalence • False positive test results in a truly negative population • Estimating Sensitivity (SE) & Specificity (SP) by testing "known status" samples (if time permits)

  3. Exercises • Detecting one or more positive pigs in an expected NEGATIVE population • Role of sample size and target prevalence • False positive test results in a truly negative population • Estimating Sensitivity (SE) & Specificity (SP) by testing "known status" samples

  4. What you need to know to determine the sample size needed to find at least one positive animal in a herd • Target prevalence (TP) • Confidence level (CL) • Population size (PS) Sample size needed = f(TP, CL, PS) • Cannon RM, Roe RT. Livestock disease surveys: A field manual for veterinarians. AGPS, Canberra, 1982.

  5. Table of sample sizes needed based on Cannon and Roe

  6. Exercises • Detecting one or more positive pigs in an expected NEGATIVE population • Role of sample size and target prevalence • False positive test results in a truly negative population • Estimating Sensitivity (SE) & Specificity (SP) by testing "known status" samples

  7. Slide courtesy of D. Polson

  8. Exercises • Detecting one or more positive pigs in an expected NEGATIVE population • Role of sample size and target prevalence • False positive test results in a truly negative population • Estimating Sensitivity (SE) & Specificity (SP) by testing "known status" samples

  9. Acknowledgements • Dale Polson, BoehringerIngelheimVetmedica Inc., U.S

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