Investigating the insomnia severity spectrum using the Pittsburgh Insomnia Rating Scale (PIRS)

Abstract

To understand how a population natively conceptualizes insomnia along with related mental health and related disabilities, understanding how an insomnia severity spectrum operates in any given population will be a goal for sleep epidemiology. To facilitate this international goal, the comparatively theory-tolerant 65-item Pittsburgh Insomnia Rating Scale (PIRS65) had been constructed with a structure designed to mimic the classification structure of the WHO's International Classification of Functioning, Disability, and Health(ICF), while measuring insomnia symptoms comprehensively. The PIRS65 underwent validation tests using both Classical Test Theory (CTT) and Item Response Theory (IRT) analyses in a research clinic-based case-control study in a North American sample. These analyses indicated that the insomnia was mostly unidimensional, but with correlations to sleep-item-free measures of fatigue, depression, and anxiety. The PIRS65’s sleep clock-time items, posed as metrics of psychological disability, performed poorly as such, despite good external validation against prospective sleep logs. PIRS65 item stems with symptom attribution to a time pattern of “not sleeping well” had the highest IRT discrimination parameters, pointing to how these respondents understood their disability from insomnia. Accordingly, a 2-item PIRS2 is proposed as particularly applicable to epidemiological studies for which an insomnia metric needs to be concise. IRT item parameters for all PIRS65 items are also provided as benchmark data for possible later international comparisons of insomnia severity spectra.

Keywords

• Insomnia
• Spectrum
• Disability
• Scale
• Validation
• Epidemiology