When not to
If the odds ratio for the result is not significant (lower odds ratio confidence interval ≤ 1), then it is unwise to bother with the confidence intervals for the NNT  see Mulrow's excellent paper [4] featured in
Bandolier 15
.
References
 Sackett DL, Haynes RB, Guyatt GH, Tugwell P. Clinical Epidemiology: a basic science for clinical medicine. Boston: Little, Brown, 1991.
 Cook RJ, Sackett DL. The number needed to treat: a clinically useful measure of treatment effect. British Medical Journal 1995; 310: 4524.
 Gardner MJ, Altman DG. Statistics with confidence. London: British Medical Journal, 1989.
 CD Mulrow, JA Cornell, CR Herren, A Kadri, L Farnett, C Aguilar. Hypertension in the elderly. Implications and generalizability of randomized controlled trials. Journal of the American Medical Association 1994 272:19328.
