title: A simple formula for the calculation of sample size in pilot studies.
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.
authors.affiliation: Department of Psychiatry and Psychology, MHeNS School for Mental Health and Neuroscience, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Viechtbauer
authors.affiliation: Department of Epidemiology, CAPHRI School for Public Health and Primary Care, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Luc
authors.initials: L
authors.lastname: Smits
authors.affiliation: 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.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kotz
authors.affiliation: Department of Midwifery Education and Studies, Research Centre for Midwifery Science, Zuyd University, PO Box 1256, 6201 BG Maastricht, The Netherlands.
authors.forename: Luc
authors.initials: L
authors.lastname: Budé
authors.affiliation: 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.
authors.forename: Mark
authors.initials: M
authors.lastname: Spigt
authors.affiliation: Department of Methodology and Statistics, CAPHRI School for Public Health and Primary Care, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands.
authors.forename: Jan
authors.initials: J
authors.lastname: Serroyen
authors.affiliation: 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.
authors.forename: Rik
authors.initials: R
authors.lastname: Crutzen
mesh_terms: D006801:Humans; D055641:Mathematical Concepts; D010865:Pilot Projects; D018401:Sample Size
keywords: Pilot study; Problem detection; Rule of three; Sample size; Unforeseen problems