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The recent report by Hull et al¹ describing the preoperative vs postoperative initiation of low-molecular-weight heparin (LMWH) prophylaxis in patients undergoing elective hip replacement provides an excellent example of the clinical usefulness of a meta-analysis. The number needed to treat (NNT) is a term that is gaining importance in assessing therapy. It is defined as the number of patients needed to treat to achieve 1 favorable outcome.² The number needed to treat is calculated as l divided by the absolute risk reduction and is a better measure of clinical significance than relative risk reduction and statistical significance.³ One other strength of NNT is that it can also be defined to describe adverse effects of treatment (ie, number needed to harm [NNH]).

The following important question still needs to be addressed: would preoperative vs postoperative use of LMWH result in a decrease in the incidence of deep vein thrombosis (DVT) in . . . [Full Text of this Article]