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Biostatistics Case Studies 2010

Biostatistics Case Studies 2010. Session 4: Evaluation of Diagnostic Tests. Peter D. Christenson Biostatistician http://gcrc.labiomed.org/biostat. Question #1. Question #2. N=40 Pheo and N=100 Not Pheo + Pred Value = + Cases / + Preds = 40/140=29%

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Biostatistics Case Studies 2010

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  1. Biostatistics Case Studies 2010 Session 4: Evaluation of Diagnostic Tests Peter D. Christenson Biostatistician http://gcrc.labiomed.org/biostat

  2. Question #1

  3. Question #2 N=40 Pheo and N=100 Not Pheo + Pred Value = + Cases / + Preds = 40/140=29% – Pred Value = – Cases / – Preds = ? Pred Values depend on population prevalence

  4. Pred Values depend on population prevalence: + Pred Value = + Cases / + Preds – Pred Value = – Cases / – Preds Not necessarily generalizable Clinically useful Sensitivity and Specificity do not depend on population prevalence: Sensitivity = + Preds / + Cases Specificity = – Preds / – Cases Generalizable Not as clinically useful

  5. Question #3

  6. Question #3 CGA moderate, say 300 Receiver Operating Characteristic Curve CGA low, say 100 AUC = 50% CGA high, say 1000 Area under ROC curve for CGA = Probability that a case has a higher value for CGA than a non-case.

  7. Question #4 • General criteria for comparing 2 diagnostic tests: • for screening: sensitivity • (2) for follow-up diagnosis: specificity or area • (3) without priority being given to sensitivity or specificity: area under ROC curve

  8. Question #5 Likelihood Ratios: + Preds / + Cases + Likelihood Ratio = + Preds / - Cases - Preds / - Cases – Likelihood Ratio = - Preds / + Cases So, +LR is how much more likely a case will test positive, relative to a non-case.

  9. Question #5 More Useful Interpretation: Post-test Odds of Case + Likelihood Ratio = Pre-test Odds of Case Post-test Odds of Non-case – Likelihood Ratio = Pre-test Odds of Non-case Like sensitivity or specificity, likelihood ratios do not depend on population prevalence and they are also more clinically useful.

  10. Question #6 CGA>270 may have been chosen to maximize the + likelihood ratio.

  11. Question #7

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