The Sleep Condition Indicator: reference values derived from a sample of 200 000 adults.

The Sleep Condition Indicator (SCI) is an eight-item rating scale that was developed to screen for insomnia disorder based on DSM-5 criteria. It has been shown previously to have good psychometric properties among several language translations. We developed age- and sex-referenced values for the SCI to assist the evaluation of insomnia in everyday clinical practice. A random sample of 200 000 individuals (58% women, mean age: 31 ± 13 years) was selected from those who had completed the SCI via several internet platforms. Descriptive and inferential methods were applied to generate reference data and indices of reliable change for the SCI for men and women across the age deciles 16-25, 26-35, 36-45, 46-55, 56-65 and 66-75 years. The mean SCI score for the full sample was 14.97 ± 5.93. Overall, women scored worse than men (14.29 ± 5.83 versus 15.90 ± 5.94; mean difference: -1.60, η2  = 0.018, Cohen's d = 0.272) and those of older age scored worse than those younger (-0.057 points per year, 95% confidence interval (CI): -0.059 to -0.055) relative to age 16-25 years. The Reliable Change Index was established at seven scale points. In conclusion, the SCI is a useful instrument for clinicians and researchers that can help them to screen for insomnia, compare completers to individuals of similar age and sex and establish whether a reliable change was achieved following treatment.