Chapter 1-statistics.txt

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Chapter 1-statistics.txt
2010-08-11 21:49:46
Stockham Scott Vet Clin Path

Chapter 1
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  1. What is the minimum # of subjects required to establish a reference interval? (according to this text)
  2. Reference limits for data showing a normal distribution are calculated values representing what?
    Mean+/- 2 SD
  3. What is the likelihood of one value falling outside the Ref. Int?
  4. T/F: Reference intervals represent results expected in all healthy animals.
    F represents expected results in 95% of healthy animals
  5. "Why is ""reference range"" and inappropriate term?"
    b/c statistically it means the difference b/w the high and low values
  6. T/F: Analytical precision is the ability of an assay to get the same result if the same sample is analyzed several times
  7. "Calculate the CV for the following diagnostic tests. Test A: Mean=10, SD=3, Test B: Mean=50, SD=4"
    "A:30%, B:8%" CV=(SD/Mean)x100
  8. Which test is more precise?
    B low CV-> high prec
  9. T/F: Within-assay CV represents random error w/in a run of the assay and the error from additional runs of the assay on the same sample.
    F That is between-assay CV
  10. "If a clinical decision is based on a minimal change in the value of an analyte, should the CV be high or low?"
  11. What term represents the ability of a test to produce a change in the signal for a defined change of the quantity?
    Analytical Sensitivity
  12. Define accuracy.
    the closeness of the agreement b/w the measured value and the true value
  13. Define analytical specificity
    ability to detect only the substance of interest freedom from interference
  14. T/F: A test w/ high diagnostic specificity is a good screening test.
    "F, screening tests should have high sensitivity"
  15. A test w/ high diagnostic sensitivity has few (FN/FP) results. Choose one
  16. Define positive predictive value.
    the probablitiy that a positive test indicates that the animal has the disease PPV=TP/(TP + FP)
  17. "When prevalence is low, which is more likely to occur? FN or FP"
  18. A test with few FN compared to TN results has a high (PPV/NPV). Choose one.
  19. T/F: The clinical value of the calculated diagnostic properties is influenced by prevalence.
  20. PPV is less when the disease prevalence is (high/low). Choose
  21. "Disease prevalence=10%, n=1000, sensitivity=94%, specificity=85%. Calculate TP, FP, TN, FN, PPV and NPV"
    "TP=94, FP=135, TN=765, FN=6, PPV=41%, NPV=99%"
  22. What happens to the PPV when the prevalence increases to 25%?
    It increases b/c TP increase and FP decrease