EBM Guidebook

Table of Contents

Title Page

1. Introduction
2. STEP 1: Formulating the Question
   
   1. POEM
   2. PICO
3. STEP 2: Finding the Best Evidence
4. STEP 3: Appraising the Evidence
   
   1. CAMeL General Steps
   2. CAMeL Critical Appraisal Protocols
      
      1. Therapy
      2. Diagnostic Tests
      3. Review Articles
      4. Screening Tests
      5. Prognosis
      6. Causation
5. STEP 4: Preparing an EBM Presentation
   
   1. Protocol for the Presentation
   2. Sample Presentation
6. Overview of Statistics
   
   1. Statistics Without Statistics
   2. Ten Ways to Cheat
7. Glossary of Terms
   Terms marked with an asterisk (*)
   are defined in the Glossary.
References

  Back to Evidence-Based Instruction page

IV.  STEP 3: Appraising the Evidence  (continued)

1. Questions to Evaluate a Study Whose Primary Objective is to Evaluate a Therapy (continued)

CER (Control Group Event Rates or % bad outcomes)	Measured in trial
EER (Experimental Group Event Rates or % bad outcomes)	Measured in trial
RRR (Relative Risk Reduction)    The percent by which risk was reduced.	(CER-EER) / CER
ARR (Absolute Risk Reduction)    The percent of patients who actually benefitted	CER-EER
NNT (Number Needed to Treat)    The number one needs to treat to provide benefit to one patient.	1/ARR

For example: 1000 patients are treated with a new medication to prevent recurrent heart attacks. The CER in the placebo group is 4%. The EER in the treatment group is 2%. Both are measured from the study. Therefore, RRR = 50%; ARR = 2%, NNT = 50. You must treat 50 patients to prevent 1 recurrent event. The rationality of this approach depends on the significance of the disease, the cost and side effects of the treatment, and the acceptability to the patient.

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