HYPOTHESIS

How the type of risk reduction influences required sample sizes in randomised clinical trials

K Bruynesteyn, A Wanders, R Landewé, D van der Heijde

Department of Internal Medicine, Division of Rheumatology, University of Maastricht, Maastricht, The Netherlands

Correspondence to:
Professor D van der Heijde
Department of Internal Medicine, Division of Rheumatology, University Hospital Maastricht, PO Box 5800, 6202 AZ Maastricht, The Netherlands; dhe{at}sint.azm.nl

To increase change between groups, randomised clinical trials (RCT) often include patients with high risk for a particular outcome, by inclusion criteria that select predictors for that outcome. This increases the statistical power, and fewer patients are required for that RCT. The way in which patient selection influences the power, and thus sample size required, depends on how an intervention reduces the individual risk: by an absolute or relative risk reduction model.

Abbreviations: ARR, absolute risk reduction; CsA, ciclosporin A, DMARDs, disease modifying antirheumatic drugs; MTX, methotrexate; RA, rheumatoid arthritis; RCT, randomised controlled trial; RRR, relative risk reduction; SSZ, sulfasalazine

Keywords: rheumatoid arthritis; radiography; joint damage; sample size; risk reduction; randomised clinical trials

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This article has been cited by other articles:

• Bruynesteyn, K, Landewe, R, van der Linden, S., van der Heijde, D (2004). Radiography as primary outcome in rheumatoid arthritis: acceptable sample sizes for trials with 3 months' follow up. Ann Rheum Dis 63: 1413-1418 [Abstract] [Full Text]