Materials and Methods
Sample
A convenience sample of 41 patients with stable COPD
(FEVi = 1.08 L [±0.55], FEVl5 percent predicted = 35.8%
[±16.6]) from two sites participated in the study. Based on
Cohen's standard approach for correlation,22 anticipating a mod¬
erate effect size, the sample size is adequate to achieve the
purpose of evaluating universal similarities of fatigue in this
population from two international sites. The study was approved
by the Human Subjects Review Board at the University of
California, Davis and the Medical Ethics Committee of the
University Hospital Groningen, the Netherlands. Written in¬
formed consent was obtained from each patient.