Number Needed To Harm (NNH) - How To Calculate It

Olly Tree Applications presents USMLE Biostatistics... a unique, yet easy to use study tool for the USMLE. It is completely free and comes with absolutely no advertisements.

Currently only on Android


Our 2x2 sample table allows for quick calculations of up to 25 different biostatistics. Simply enter the required data into the highlighted boxes and the solution will appear. All of the most important equations are here – from absolute risk reduction to odds ratio to specificity.

As your knowledge and understanding of medical biostatistics grows, we suggest that you become accustomed to solving questions without the use of our 2x2 sample table. Also be sure to check out our flashcards, board review questions, and video lectures.

Key Concept:

So you want to change a patient’s current therapy because a new medication has a decreased risk of a particular side effect. That sounds reasonable, but have you taken other issues into consideration (e.g., efficacy, other adverse reactions, cost, etc.)? And how about the number needed to treat? Do you know how many patients would need to receive the new therapy as opposed to the old one before one patient less experiences the side effect? Determining the number needed to treat can be useful in clinical practice when analyzing the risk versus benefit between two therapies.

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