Calculate the number needed to treat and compare it against harms.
Comparing the number needed to treat against the number needed to harm gives the likelihood of being helped rather than harmed. A ratio well above one is required for a treatment to be worthwhile. Treatments with a favourable NNT can still be net harmful if the NNH is lower, which is why both must be reported together.
Number Needed to Treat
NNT = 1 ÷ ARR; NNH = 1 ÷ absolute risk increase; LHH = NNH ÷ NNT
NNT = 1 ÷ ARR; NNH = 1 ÷ absolute risk increase; LHH = NNH ÷ NNT Comparing the number needed to treat against the number needed to harm gives the likelihood of being helped rather than harmed. A ratio well above one is required for a treatment to be worthwhile.
Treatments with a favourable NNT can still be net harmful if the NNH is lower, which is why both must be reported together.
This calculator takes 4 inputs: Control event rate, Treatment event rate, Adverse event rate without treatment, Adverse event rate with treatment. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.