Number Needed To Harm

Number Needed To Harm

The number needed to harm (NNH) is an epidemiological measure that indicates how many patients need to be exposed to a risk-factor over a specific period to cause harm in one patient that would not otherwise have been harmed. It is defined as the inverse of the attributable risk. Intuitively, the lower the number needed to harm, the worse the risk-factor.

NNH is similar to Number needed to treat (NNT), where NNT usually refers to a therapeutic intervention and NNH to a detrimental effect or risk factor. NNH is computed with respect to "exposure" and "non-exposure", and can be determined for raw data or for data corrected for confounders. A defined endpoint has to be specified. If the probabilities pexposure and pnon-exposure of this endpoint are known, then the NNH is computed as 1/(pexposure-pnon-exposure).

The NNH is an important measure in evidence-based medicine and helps physicians decide whether it is prudent to proceed with a particular treatment which may expose the patient to harms while providing therapeutic benefits. If a clinical endpoint is devastating enough without the drug (e.g. death, heart attack), drugs with a low NNH may still be indicated in particular situations if the number needed to treat, (the converse for side effects, or the drug's benefit) is less than the NNH. However, there are several important problems with the NNH, involving bias and lack of reliable confidence intervals, as well as difficulties in excluding the possibility of no difference between two treatments or groups.

Read more about Number Needed To Harm:  Worked Example, Number of Exposures Needed To Harm

Other articles related to "number needed to harm, number, needed to harm, harm":

Number Needed To Harm - Number of Exposures Needed To Harm
... In case there can be more than one exposure in the specific period, the number (of patients) needed to harm is numerically equal to number of exposures needed to harm for one person if the risk per ... when the risk per exposure is very small or the "harm" is a very brief disease that doesn't confer immunity ...

Famous quotes containing the words harm, number and/or needed:

    Probably the greatest harm done by vast wealth is the harm that we of moderate means do ourselves when we let the vices of envy and hatred enter deep into our own natures.
    Theodore Roosevelt (1858–1919)

    Of all reformers Mr. Sentiment is the most powerful. It is incredible the number of evil practices he has put down: it is to be feared he will soon lack subjects, and that when he has made the working classes comfortable, and got bitter beer into proper-sized pint bottles, there will be nothing left for him to do.
    Anthony Trollope (1815–1882)

    I needed a drink, I needed a lot of life insurance, I needed a vacation, I needed a home in the country. What I had was a coat, a hat and a gun.
    Raymond Chandler (1888–1959)