Chapter 4 Review Questions (Key)

1. Reproducibility refers to repeatability or consistency of a test (or evaluation) from one use to the next. Validity is the ability to accurate discriminate (between people with and without disease).
2. Symptom = experienced by a patient; Sign = observation made by examiner. 
   Nausea = symptom ( experienced by patient, not directly observable) 
   Vomiting = symptom
   Red throat is a sign (observed by an examiner)
   Sore throat = symptom
3. Kappa
4. Kappa measures percent agreement above chance. A good deal of simple agreement is often merely by chance.
5. False. A kappa of 0 indicates random agreement
6. Definitions. Let D = disease status and T = test status. Thereby: (a) TP = D+ and T+ (b) TN = D- and T-  (c) FP = D- and T+ (d) FN = D+ and T-  
7. (a) Specificity ~= Pr(T-| D-) 
   (b) Sensitivity ~= Pr(T+|D+) 
   (c) PVP ~= Pr(D+|T+) 
   (d) PVN ~= Pr(D-|T-) 
8. SEN
9. PVN
10. Prevalence, SEN, and SPEC
11. Because most people tested will be disease free and using even a specific test in such a population results in many false positives (e.g., if you use a test that is 99% SPECific in a million healthy people, you will derive  0.01 × 1,000,000 = 10,000 false positives).
12. It will decrease the number of FNs, increase SENsitivity, and decrease SPECicity. 
13. High sensitivity; you don't want to miss any cases.