# Biostats 2

 What's Pre-test probability? probability of the disease before a test is done (basically the prevalence) What's Post-test probability based on outcome of the test, the likelihood that the patient has the disease (rule in/out) What's the table look like for Likelihood Ratios? What's a positive likelihood ratio? ration or proportion of those with disease & test positive: without disease with positive test result (1-specificity) What's the calculation for the positive likelihood ratio? What's a Negative likelihood ration? Ration = those with disease & negative test result : without disease and negative test result (specificity) What's the equation for the negative likelihood ratio? What are the components of framing a clinical question? P - patient/population being addressedI - intervention in questionC - comparison (when relevant)O - outcome of outcomes of interest What's the significance of LR >10 or <0.1? Generate large and conclusive changes from pre-test andpost-test probability. What's the significance of LR of 5-10 and 0.1-0.2? Generate moderate shifts in pre-test to post-test probability. 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. What's the significance of LR of 1-2 and 0.5-1? Alter probability to a small (a likely insignificant) degree What's a decision analysis? Formal structure integrating evidence (beneficial/harmful effects) with values, preference, probablilitys, costs associated What do squares, circles, and triangles represent on a decision analysis? Square- decisionCircle - chance eventsTriangle - outcome nodes When are dignostic tests useful? When there are large changes between pre-test and post-test probability; validity compared to 'gold standard' What factors affect predicitve valies the most? prevalenceof disease, sensitivity, specificity What are the advantages of LRs? Contribution of test result as a single numberDetermining post -test probablilty given a resultSummarizing informationDescribing probability of disease What's the effect of having a low cut-off level on sensitivity/specificy? Increase sensitivity What's the effect of raising the cut-off level on specificity/sensitivity? Increased sensitivity Authoreschott ID79009 Card SetBiostats 2 DescriptionEvidence based medicine Updated2011-04-12T03:23:25Z Show Answers