The calculation of NNH is the same as that of
NNT, but the interpretation is differentiated by
the adverse outcomes present in harm studies.
Here the term NNH effectively replaces NNT.
Similarly Absolute Risk Increase (ARI) is
calculated in the same way that ARR is calculated
but the intervention
increases the amount of
harm instead of therapeutic gain.
NNH = 1/ARI = 1/|CER – EER|