Measurement properties of the Shiftwork Survey and Standard Shiftwork Index.

The Shiftwork Survey (SS) was introduced, along with the Standard Shiftwork Index (SSI), to provide a set of standardized self-report measures to be used in shiftwork research. However, beyond the initial assessment, no attempt has been made to examine the measurement properties of these scales in an independent sample of shiftworkers. Our goal, therefore, was to examine the measurement properties of these scales in an industrial sample of primarily male shiftworkers (N = 370). We found that all scales had acceptable reliabilities (alphas). The confirmatory factor analyses revealed that the chronic fatigue, coping, job satisfaction, and sleep scales are the weakest psychometrically, and the anxiety, personality (extraversion, neuroticism), general health, and physical health scales are the strongest psychometrically. Using item response theory analyses, we found that the scales overall are generally adequate measures of their underlying constructs, although many items should be altered or omitted. Our results, however, are limited by reliance on a single sample.