I have performed similar NNT calculations on the Fracture Intervention
Trial, arm 2 for women with low BMD but no pre-existing vertebral fractures.
I think what Mick calculated might be put like this:
3 year NNT (prevent one hip fracture) =
91 (59 to 4545) or
91 (59 to infinity) or
91 (59 to no benefit),
meaning that the point estimate for the NNT for the efficacy may be 91, or
as low as 59 to no efffect at all.
When one of the confidence limits approaches infinity, this is usually so
because the difference between groups is not statistically significant.
I think the implications of this finding is very interesting, because it
gives us a new way of thinking treatment effects. Where dichotomising at a
significance level of p<0.05 is the traditional way of looking at "effect
or no effect", it seems that the NNT gives us a more useful point estimate
with a confidence interval which may include no effect.
I have calculated the NNTs for the FIT-II study and present them at my
website:
http://www.uib.no/isf/people/atle/fit2.htm
Atle Klovning, MD, Research Fellow,
Specialist in General Practice/Family Medicine
Div. for General Practice,
University of Bergen, Norway
(+47) 55 58 67 09
(+47) 55 58 67 10 (FAX)
http://www.uib.no/isf/people/atle/
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|