Sample Size and Power Calculation
Before this study, we collected data from 16 shift workers in a pilot study. The mean sleep duration was 334.68 (SD 135.1) minutes. On the basis of the pilot study data with a small sample, the mean sleep duration at week 4 of the intervention was assumed to be 30 minutes longer, with no change in SD. Assuming a 2-sided level of significance of 5%, power of 80%, and correlation coefficient of 0.8, using the SAS system (SAS Institute Inc), 66 participants were required for a significant difference to be found in the 2-tailed paired 