reciprocal of difference number needed to harm NNTH NNH number needed to treat to harm https://www.cebm.ox.ac.uk/resources/ebm-tools/glossary A statistic that represents the number of units that, if treated or exposed to the intervention, lead to one additional undesired outcome. The Number Needed to Harm is calculated as the reciprocal of a treatment effect estimate, where the effect estimate is expressed as a risk difference. requires discussion