Biostats 2

  1. What's Pre-test probability?
    probability of the disease before a test is done (basically the prevalence)
  2. What's Post-test probability
    • based on outcome of the test, the likelihood that the
    • patient has the disease (rule in/out)
  3. What's the table look like for Likelihood Ratios?
    Image Upload 1
  4. What's a positive likelihood ratio?
    ration or proportion of those with disease & test positive: without disease with positive test result (1-specificity)
  5. What's the calculation for the positive likelihood ratio?
    Image Upload 2
  6. What's a Negative likelihood ration?
    Ration = those with disease & negative test result : without disease and negative test result (specificity)
  7. What's the equation for the negative likelihood ratio?
    Image Upload 3
  8. What are the components of framing a clinical question?
    • P - patient/population being addressed
    • I - intervention in question
    • C - comparison (when relevant)
    • O - outcome of outcomes of interest
  9. What's the significance of LR >10 or <0.1?
    • Generate large and conclusive changes from pre-test and
    • post-test probability.
  10. What's the significance of LR of 5-10 and 0.1-0.2?
    Generate moderate shifts in pre-test to post-test probability.
  11. What's the significance of LR of 2-5 and 0.5-0.2?
    Generate small (but sometimes important) shifts from pre- to post-test probability.
  12. What's the significance of LR of 1-2 and 0.5-1?
    Alter probability to a small (a likely insignificant) degree
  13. What's a decision analysis?
    Formal structure integrating evidence (beneficial/harmful effects) with values, preference, probablilitys, costs associated
  14. What do squares, circles, and triangles represent on a decision analysis?
    • Square- decision
    • Circle - chance events
    • Triangle - outcome nodes
  15. When are dignostic tests useful?
    When there are large changes between pre-test and post-test probability; validity compared to 'gold standard'
  16. What factors affect predicitve valies the most?
    prevalenceof disease, sensitivity, specificity
  17. What are the advantages of LRs?
    • Contribution of test result as a single number
    • Determining post -test probablilty given a result
    • Summarizing information
    • Describing probability of disease
  18. What's the effect of having a low cut-off level on sensitivity/specificy?
    Increase sensitivity
  19. What's the effect of raising the cut-off level on specificity/sensitivity?
    Increased sensitivity
Card Set
Biostats 2
Evidence based medicine