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This letter provides misleading advice. It doesn't make sense to
apply a number
needed to treat (NNT) from a meta-analysis that includes trials with
differing populations that have widely differing underlying likelihoods of
The NNT is based on the absolute risk reduction, not a relative one (which
more constant and therefore makes sense for applying in a meta-analysis).
the underlying risk varies widely, say from primary prevention trials
(such as the
JUPITER trial) to diabetes patients (such as the HPS), then the NNT
spurious estimate of the number of people needed to be treated to prevent
event. Absolute risks really aren't useful in most meta-analyses.