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The amount of change in quality of sleep (QOS), as measured by a 100-mm visual analog scale (VAS), that constitutes a minimum clinically significant difference was determined. A total of 428 patients with insomnia aged 55 years and older received placebo (2 weeks), prolonged release melatonin 2 mg (3 weeks) and then placebo (2 weeks). Sleep quality was assessed by the end of each period using the Leeds Sleep Evaluation Questionnaire (LSEQ) QOS variable and a five-point severity-rating scale. The mean difference between current and preceding VAS scores in patients improving or worsening by 1 point was 13 mm (95% CI 11-16). Correlation analysis indicated that a change of 1 point was associated with a mean change of 10.3 mm on the VAS. In conclusion, a change of 10 mm change in the 100-mm VAS QOS variable of the LSEQ, signifies an important change in patients' sleep quality.
Zisapel et al. (Mon,) studied this question.