Decision Analysis in Clinical Guidelines: Net Benefit, NNT, & NRI

RRR (Relative Risk Reduce) ＝ 1 - Relative risk ( because P(ASCVD|Tx) is less than P(ASCVD|No Tx) ),

so RRR ＝ 1 - P(ASCVD|Tx) / P(ASCVD|No Tx) ＝ ( P(ASCVD|No Tx) - P(ASCVD|Tx) ) / P(ASCVD|No Tx),

P(ASCVD|No Tx) - P(ASCVD|Tx) is the ARR,

so RRR ＝ ARR / P(ASCVD|No Tx), ARR ＝ RRR * P(ASCVD|No Tx).

I guess that 3% is the P(ASCVD|No Tx).

so NNT ＝ 1 / (3% 35%) ≈ 100 (NND)

NNT ＝ 1 / (7% * 45%) ≈ 33 (NND)

NND is number-needed-to-treat to cause 1 case of incident diabetes in 10 years according to that guideline.

I guess this is how it’s used.

NNT is a key term in national medical licensing examination in country I worked. But to be honest, I have never seen its use in clinical guidelines in country I worked. My experience is limited; I always assumed it was a brain teaser aimed to torment students during the exam.

I am curious to hear what others think about this usage.