Economics notes: Cost effectiveness calculations and sample size

doi:10.1136/bmj.321.7262.697

BMJ 2000;321:697 ( 16 September )

Education and debate

Economics notes

Cost effectiveness calculations and sample size

This is one of an occasional series of notes on economics

David J Torgerson, senior research fellow ^a, Marion K Campbell, senior statistician ^b.

^a Centre for Health Economics, University of York, York YO1 5DD, ^b Health Services Research Unit, University of Aberdeen, Aberdeen AB25 2ZD

Correspondence to: D J Torgerson
The first 150 words of the full text of this article appear below.

Clinical trials should be large enough to detect a clinically important difference between two treatments. Yet a clinicallyimportant difference is often difficult to define and debatable.This difficulty may explain why so few published trials reportthe clinical reasoning underlying their sample size selection.Furthermore, clinical investigators are often suspected of approachingsample size calculations logistically rather than clinically:they estimate the number of patients who can be recruited intoa trial and then ask a statistician to justify the sample sizeby calculating the "detectable" difference implied by the numberof recruitable patients.¹ Including economic criteria to aidsample size determination for clinical trials might improve therigour of sample size selection. ² ³

Consider a recent randomised trial comparing the effectiveness of hysterectomy with hysteroscopic surgery for treating menorrhagia. ⁴ ⁵ The trial found that hysteroscopic surgery was an acceptable alternativeto hysterectomy but had a considerable retreatment rate. It was. . . [Full text of this article]

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