Effectiveness Research and Implications for Study Design

Sample Size and Statistical Power

by Roland Sturm, Jurgen Unutzer, Wayne J. Katon

Purchase Print Copy

 FormatList Price
Add to Cart Paperback10 pages Free

Most clinical trials have started to incorporate more broadly defined outcome measures, such as health-related quality of life, to complement clinical status measures as well as direct costs and cost-effectiveness analyses. Contrasting a broad range of outcome and cost measures, the authors analyze the implications for sample sizes and study design using data from prior mental health and primary care studies that span a wide range of practice settings, patient populations and geographic areas. While meaningful clinical symptomatic differences are often detectable with sample sizes of well under 100 per cell, detecting even large changes in health-related quality of life generally requires several hundred observations per cell. Reasonable precision in cost estimates usually requires sample sizes in the thousands. Very few clinical trials or observational effectiveness studies that incorporate quality-of-life or cost measures have such sample sizes, resulting in many (unreported) null findings and, due to publication biases favoring significant results, scientific publications that exaggerate true effects. This raises issues for the general direction of clinical trials and effectiveness studies, as well as for how cost and health-related quality of life results based on small studies should be dealt with in publications.

Originally published in: General Hospital Psychiatry, v. 21, 1999, pp. 274-283.

This report is part of the RAND Corporation reprint series. The Reprint was a product of the RAND Corporation from 1992 to 2011 that represented previously published journal articles, book chapters, and reports with the permission of the publisher. RAND reprints were formally reviewed in accordance with the publisher's editorial policy and compliant with RAND's rigorous quality assurance standards for quality and objectivity. For select current RAND journal articles, see External Publications.

The RAND Corporation is a nonprofit institution that helps improve policy and decisionmaking through research and analysis. RAND's publications do not necessarily reflect the opinions of its research clients and sponsors.