When calculating the NNT for a treatment that is barely statistically
significant and has a large NNT, the confidence interval is wide and very
asymmetrical. For example in women with prior vertebral fractures and
femoral neck BMD at least 2.1 standard deviations below young normal, the
NNT with alendronate for 3 years to prevent one hip fracture =91 (95% CI
59-4545)
I assume that if I were to able to calculate a mean NNT, it would be higher
than 91, perhaps 200-300. Is their a formula for recalulating the NNT to
adjust for this asymmetry? and is this a reasonable thing to do?
Thanks
Mick Braddick
Clinical Epidemiologist
Group Health Cooperative
Seattle
USA
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