# Biostats 2

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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?
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?
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?
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
 Author: eschott ID: 79009 Card Set: Biostats 2 Updated: 2011-04-12T03:23:25Z Folders: Description: Evidence based medicine Show Answers: