A simple formula for the calculation of sample size in pilot studies

Wolfgang Viechtbauer; Luc Smits; Daniel Kotz; Luc Budé; Mark Spigt; Jan Serroyen; Rik Crutzen

doi:10.1016/j.jclinepi.2015.04.014

A simple formula for the calculation of sample size in pilot studies

J Clin Epidemiol. 2015 Nov;68(11):1375-9. doi: 10.1016/j.jclinepi.2015.04.014. Epub 2015 Jun 6.

Authors

Wolfgang Viechtbauer¹, Luc Smits², Daniel Kotz³, Luc Budé⁴, Mark Spigt⁵, Jan Serroyen⁶, Rik Crutzen⁷

Affiliations

¹ Department of Psychiatry and Psychology, MHeNS School for Mental Health and Neuroscience, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
² Department of Epidemiology, CAPHRI School for Public Health and Primary Care, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
³ Department of Family Medicine, CAPHRI School for Public Health and Primary Care, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands; Institute of General Practice, Medical Faculty, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.
⁴ Department of Midwifery Education and Studies, Research Centre for Midwifery Science, Zuyd University, PO Box 1256, 6201 BG Maastricht, The Netherlands.
⁵ Department of Family Medicine, CAPHRI School for Public Health and Primary Care, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands; Department of Community Medicine, General Practice Research Unit, University of Tromsø, Tromsø, Norway.
⁶ Department of Methodology and Statistics, CAPHRI School for Public Health and Primary Care, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
⁷ Department of Health Promotion, CAPHRI School for Public Health and Primary Care, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands. Electronic address: rik.crutzen@maastrichtuniversity.nl.

PMID: 26146089
DOI: 10.1016/j.jclinepi.2015.04.014

Abstract

One of the goals of a pilot study is to identify unforeseen problems, such as ambiguous inclusion or exclusion criteria or misinterpretations of questionnaire items. Although sample size calculation methods for pilot studies have been proposed, none of them are directed at the goal of problem detection. In this article, we present a simple formula to calculate the sample size needed to be able to identify, with a chosen level of confidence, problems that may arise with a given probability. If a problem exists with 5% probability in a potential study participant, the problem will almost certainly be identified (with 95% confidence) in a pilot study including 59 participants.

Keywords: Pilot study; Problem detection; Rule of three; Sample size; Unforeseen problems.

MeSH terms

Humans
Mathematical Concepts
Pilot Projects*
Sample Size*