The Journal of Bone and Joint Surgery (American). 2009;91:35-40.
doi:10.2106/JBJS.H.01602
© 2009 The Journal of Bone and Joint Surgery, Inc.
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Outcome Measures and Implications for Sample-Size Calculations

Michael Zlowodzki, MD1 and Mohit Bhandari, MD, MSc, FRCSC2

1 Department of Orthopaedic Surgery, University of Minnesota, 2450 Riverside Avenue South, R200, Minneapolis, MN 55454. E-mail address: zlowo001{at}umn.edu
2 Division of Orthopaedic Surgery, Department of Surgery, McMaster University, 293 Wellington Street North, Suite 110, Hamilton, ON L8L 2X2, Canada. E-mail address: bhandam{at}mcmaster.ca

Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

This article focuses on items to consider when selecting outcome measures for a clinical study. The choice of outcome measures depends largely on the research question and the study design. Sample-size requirements can vary greatly, depending on the type and the number of outcome measures selected. In this paper, we review the differences between categorical and continuous outcomes as well as the differences between primary and secondary outcomes and we discuss the concept of minimally important differences and the problems associated with composite outcomes. We also provide instruction on how to conduct and present a sample-size calculation.


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