How to Calculate NNT (Number Needed to Treat) for USMLE: A Complete Guide
Number Needed to Treat (NNT) tells you how many patients need to receive a treatment for one additional patient to benefit compared to the control group. NNT = 1 / ARR where ARR = Control Event Rate - Experimental Event Rate.
Step-by-Step Calculation
1. Calculate ARR = CER - EER. 2. Calculate NNT = 1 / ARR. 3. Always round UP to the next whole number.
Critical Rules for USMLE
- Always round UP — you cannot treat a fraction of a patient
- NNT is time-dependent
- Lower NNT = more effective treatment
- NNH uses the same formula for adverse outcomes