Psychometric Properties of the Sleep Locus of Control (SLOC) Scale in a Portuguese Sample

Over the past few decades, research has suggested that cognitive variables play a key role in sleep disorders, particularly, in insomnia. The SLOC (Sleep Locus of Control Scale) evaluates the sleep locus of control, which is associated with the degree to which an individual attributes her/his experiences of sleep to chance or internal causes. The aim of this study was to develop the first translation and adaptation of the SLOC into the European Portuguese, as well as to analyze its psychometric properties. In this study, it was recruited a sample of 2029 Portuguese Higher Education students, aged ≥ 18 years, where approximately 75% of the sample were women and 25% men. The results showed that the SLOC had acceptable internal consistency value (α = .64), considering that it is a measure with a reduced number of items. As in the original study, a principal component analysis with varimax rotation identified two components. A parallel analysis was also conducted, identifying two factors. The correlation between the two subscales "internal sleep locus of control" and "chance sleep locus of control" was positive albeit of low magnitude (r = .15). Through the analysis carried out, it was also observed that individuals with "insomnia", relative to those without, had a more chance sleep locus of control. Overall, these findings show similarities with the original study. The SLOC seems to be a useful psychological assessment measure to be used in clinical and research settings.