Friday, March 30, 2012

Number needed to harm (NNH)


NNH represents the number of people that need to be treated for one adverse event to ocurr.
  1. Formula: NNH = 1 / ARI
    • NNT: number needed to harm
    • ARI: absolute risk increase
    • ARI = AR: atributabe risk
  2. Classic USMLE Question:
      • "You are asked to analyze survival data after six months of treatment with a drug X. The results are given below:
                                                 Alive                Dead
        Treated +                             10                  15
        Treated -                              10                  30

        What is the number needed to harm for drug X?
      • Answer
        NNH = 1 / AR
                 = 1 / (a / a+b) - (c / c+d)

        a / a + b = treatment group = 10 / (10 + 15) = 0.40
        c / c + d = placebo group = 10 / (10 + 30) = 0.25

        NNH = 1 / (0.40 - 0.25) = 1 / 0.15 = 66.6 or 67 

6 comments:

  1. THIS IS WRONG

    ReplyDelete
  2. IT SHUD BE 1/(15/25-30/40)=1/0.6-0.75=1/015=6.67

    ReplyDelete
  3. Now where's the calculations for NNR ???!! that was my actual reason for being around here..

    ReplyDelete
  4. your reasoning is sound, but shouldn't the answer be 6.66?

    1/0.15=6.667

    ReplyDelete
  5. 1/0.15= 6.7 . no? why is 67 the answer?

    ReplyDelete
  6. Excellent blog post! Stimulates me to read much more of your work. I’ll bookmark your page so I can go back here.

    www.n8fan.net

    ReplyDelete