Stats #24: What Do All These Numbers Mean? Likelihood ratios
Content: This training class will teach you some of the numbers used to describe medical diagnostic tests. This class is useful for anyone who reads journal articles that evaluate these tests.
Objectives: In this class you will learn how to:
- Calculate the likelihood ratio for a diagnostic test
- Estimate pre-test probability and odds
- Calculate post-test probabilities
- Show how changes in prevalence affect the positive predictive value
Teaching strategies: Didactic lectures and small group exercises.
IRB Education Credits: This class does not qualify for IRB Education Credits (IRBECs).
Notes: Please bring a pocket calculator. I will use the following papers in class as examples:
- Accuracy of a Single Question in Screening for Depression in a Cohort of Patients After Stroke: Comparative Study. Caroline Watkins, Leanne Daniels, Cathy Jack, Hazel Dickinson, and Martin van den Broek. BMJ 2001; 323: 1159. [Full text] [PDF]
- The SCOFF Questionnaire and Clinical Interview for Eating Disorders in General Practice: Comparative Study. Amy J Luck, John F Morgan, Fiona Reid, Aileen O'Brien, Joan Brunton, Clare Price, Lin Perry, and J Hubert Lacey. BMJ 2002; 325: 755-756. [Full text] [PDF]
- A clinical score to reduce unnecessary antibiotic use in patients with sore throat. W. J. McIsaac, D. White, D. Tannenbaum, D. E. Low. Cmaj 1998: 158(1); 75-83. [Medline] [Abstract] [PDF]
For the extended version of this class, I will also use the following page of recent weblog entries about diagnostic testing:
Outline:
- Overview of the STATS web pages
- Consulting services that I provide
- Exercises for Stats #24
- Sensitivity
- Specificity
- Positive Predictive Value
- Negative Predictive Value
- Likelihood ratio
- Fagan nomogram
- Likelihood ratio slide rule
- Please fill out an evaluation form