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Herein, what does number needed to harm mean?
The number needed to harm (NNH) is an epidemiological measure that indicates how many persons on average need to be exposed to a risk factor over a specific period to cause harm in an average of one person who would not otherwise have been harmed.
- The NNT is the inverse of the absolute risk reduction (ARR).
- The ARR is the absolute difference in the rates of events between a given activity or treatment relative to a control activity or treatment, ie control event rate (CER) minus the experimental event rate (EER), or ARR = CER - EER.
In this manner, how do you calculate number needed to harm?
From this the value known as the number needed to harm (NNH) can be calculated by dividing 1 by the absolute risk increase, and again multiplying by 100 when the ARI is expressed as a percentage. NNH shows how many individuals would need to be treated with the drug in order for 1 to show the harmful effect.
The NNT is simply the inverse of the ARR; it can be calculated by taking 100 and dividing it by the ARR (1).