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

2. Iowa State University College of Veterinary Medicine Exercises 1.Detecting one or more positive pigs in an expected NEGATIVE population –Role of sample size and target prevalence 2.False positive test results in a truly negative population 3.Estimating Sensitivity (SE) & Specificity (SP) by testing "known status" samples (if time permits)

3. Iowa State University College of Veterinary Medicine Exercises 1.Detecting one or more positive pigs in an expected NEGATIVE population –Role of sample size and target prevalence 2.False positive test results in a truly negative population 3.Estimating Sensitivity (SE) & Specificity (SP) by testing "known status" samples

4. Iowa State University College of Veterinary Medicine What you need to know to determine the sample size needed to find at least one positive animal in a herd 1.Target prevalence (TP) 2.Confidence level (CL) 3.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. Iowa State University College of Veterinary Medicine Table of sample sizes needed based on Cannon and Roe

6. Iowa State University College of Veterinary Medicine Exercises 1.Detecting one or more positive pigs in an expected NEGATIVE population –Role of sample size and target prevalence 2.False positive test results in a truly negative population 3.Estimating Sensitivity (SE) & Specificity (SP) by testing "known status" samples

7. Iowa State University College of Veterinary Medicine Slide courtesy of D. Polson

8. Iowa State University College of Veterinary Medicine Exercises 1.Detecting one or more positive pigs in an expected NEGATIVE population –Role of sample size and target prevalence 2.False positive test results in a truly negative population 3.Estimating Sensitivity (SE) & Specificity (SP) by testing "known status" samples

9. Iowa State University College of Veterinary Medicine

10. Acknowledgements Dale Polson, Boehringer Ingelheim Vetmedica Inc., U.S