Identifying advanced and delayed sleep phase disorders in the general population: a national survey of New Zealand adults.

The aim was to estimate the prevalence of, and identify independent risk factors for, Advanced (ASPD) and Delayed Sleep Phase Disorder (DSPD) among Māori (indigenous New Zealanders) and non-Māori adults using a self-report questionnaire. The Munich Chronotype Questionnaire was mailed to a stratified sample of 9100 adults (5100 Māori and 4000 non-Māori) aged 20-59 years randomly selected from the electoral rolls (54% response rate). Different definitions for ASPD and DSPD were developed using combinations of symptoms including self-reported bed and rising times, current chronotype, and a desire to change sleep schedule. Logistic regression models were used to model the likelihood of reporting ASPD or DSPD separately after adjusting for ethnicity (Māori versus non-Māori), sex (males versus females), age (in decades), socio-economic deprivation (NZDep2006 deciles) and employment status (unemployed, night work versus employed with no night work). The prevalence of ASPD ranged from 0.25% to 7.13% whereas the prevalence of DSPD was 1.51 to 8.90% depending on the definition used. The prevalence of ASPD was higher among men and increased with age. The prevalence of DSPD was higher among those living in more deprived areas and decreased with age. After controlling for ethnicity, gender, age, socio-economic deprivation and employment status, people with ASPD were more likely to report excessive daytime sleepiness, whereas those with DSPD were more likely to report poor or fair self-rated health. Reporting ASPD and DSPD were associated with self-reported night work. In this large sleep timing survey, we found no differences in the prevalence of self-identified ASPD and DSPD between Maori and non-Maori. This has implications for the development and provision of sleep health services and strategies for managing the significant impact of work patterns on sleep.