Abstract
The number needed to treat (NNT) is a popular summary statistic to describe the absolute
effect of a new treatment compared with a standard treatment or control concerning
the risk of an adverse event. The NNT concept can be applied whenever the risk of
an adverse event is compared between two groups; for the comparison of exposed with
unexposed subjects in epidemiological studies, we propose the term “number needed
to be exposed” (NNE). Whereas in randomized clinical trials NNT can be calculated
on the basis of a simple 2×2 table, in epidemiological studies methods to adjust for
confounders are required in most applications. We derive a method based upon multiple
logistic regression analysis to perform point and interval estimation of NNE with
adjustment for confounding variables. The adjusted NNE can be calculated from the
adjusted odds ratio (OR) and the unexposed event rate (UER) estimated by means of
an appropriate multiple logistic regression model. As UER is dependent on the confounders,
the adjusted NNEs also vary with the values of the confounding variables. Two methods
are proposed to take the dependence of NNE on the values of the confounders into account.
The adjusted number needed to be exposed can be a useful complement to the commonly
presented results in epidemiological studies, such as ORs and attributable risks.
Keywords
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Article info
Publication history
Accepted:
November 4,
2001
Received in revised form:
October 26,
2001
Received:
February 28,
2001
Identification
Copyright
© 2002 Elsevier Science Inc. Published by Elsevier Inc. All rights reserved.
