Valid methods for estimating children's sleep problems in clinical practice

Behavioural sleep disorders are highly prevalent in children and associated with impaired daytime functioning and significant social and psychological consequences (1–3). Thus, a careful evaluation of sleep patterns is essential for the management of children’s sleep disorders by healthcare professionals. Recently, we provided data about the interchangeable use of actigraphy, a sleep diary and sleep questionnaire for the assessment of sleep patterns in a sample of healthy kindergarten children (4). We showed that rates of agreement between diary and actigraphy, according to Bland and Altman (5), were satisfactory for sleep start, sleep end and assumed sleep, but not for actual sleep time and nocturnal wake time. However, it remains unknown how well diary and actigraphy data which are frequently used in the clinical setting agree in sleepdisordered children. To address this issue, rates of agreement between methods were calculated in a sample of sleep-disordered children recruited from our outpatient sleep clinic. Based on previous findings (4,6), we expected that for sleep start, sleep end and assumed sleep, the diary and actigraphy data would agree well in sleep-disordered children. However, we expected lower agreement between diary and actigraphy data with respect to nocturnal awakening and daytime sleep. Comparing the limits of agreement between healthy and sleep-disordered children, we hypothesised that parental reports of sleep-disordered children would be more accurate than reports of healthy children because of increased parental involvement (7). The study was approved by the Ethical Review Board of the Canton Zurich, Switzerland, and performed according to the Declaration of Helsinki. Informed written consent was obtained from all parents. Parents were requested to attach an actigraph (Actiwatch Plus , AW4, Cambridge Neurotechnology, Cambridge, UK) and to complete a diary, in 15-min intervals, over seven to 10 successive days until the first outpatient consultation. An example of this has previously been described (4). Measures derived from the diary included: a) sleep start time, defined as the beginning of the continuous line in the evening, b) sleep end time, the ending of the continuous line in the morning, c) assumed sleep, the difference between sleep start and sleep end time without excluding ‘nocturnal wake time’, d) actual sleep time, the difference between ‘assumed sleep’ and ‘nocturnal wake time’ (true sleep time), e) daytime sleep duration, the summed time of all diary reported sleep periods between sleep end time in the morning and the next sleep start time in the evening, and f) 24-h sleep duration, as the sum of ‘assumed sleep’ and ‘daytime sleep duration’. Measures derived from actigraphy included: a) sleep start, defined as the first minute of at least 3 min of scored sleep within 30 min of the diary reported bedtime, b) sleep end time, the last minute of at least 5 min of scored sleep within 30 min before the dairy reported rising time (8), c) assumed sleep, the difference between sleep start and sleep end time, d) actual sleep time, the difference between ‘assumed sleep’ and the amount of times scored as wake during the nocturnal sleep period, e) daytime sleep duration, the sum of all sleep periods of at least 10 min up to 3 h containing zero activity counts (9) and f) 24-h sleep duration, as the sum of ‘assumed sleep’ and ‘daytime sleep duration’. Socioeconomic status of the parents was calculated as a score ranging from two to 12 points, summing maternal education and paternal occupation (10). The degree of agreement between the methods was quantified using the 95% limits of agreement according to Bland and Altman (5). F-Tests for the equality of variances were calculated for differences between healthy and sleep-disordered children. Regression analyses were used to examine age effects.