title: A validation of wrist actigraphy against polysomnography in patients with schizophrenia or bipolar disorder.
abstract: OBJECTIVE
  Sleep disturbances are frequent in patients with schizophrenia or bipolar disorder. Actigraphy has been established as a generally reliable method to examine these disturbances across varying time spans, but the validity against polysomnography (PSG) is not well investigated for this population. We validated wrist-worn actigraphy against PSG in a population of chronic, medicated patients with schizophrenia or bipolar disorder.
  
  
  METHODS
  From a clinical trial, we derived data from 37 patients with schizophrenia and five patients with bipolar disorder who were examined with one-night PSG and concomitant actigraphy. The following sleep variables were compared between the two methods: total sleep time, sleep efficiency, sleep latency, number of awakenings, and time awake after sleep onset. The degree of consistency between the two methods was evaluated using the intra-class correlation coefficient and Bland-Altman plots. Subgroup analyses included splitting the analyses according to sex, diagnosis, and duration of wakefulness after sleep onset. PSG was considered the gold standard.
  
  
  RESULTS
  The intraclass correlation coefficient was high for total sleep time, moderate for the number of awakenings, and low or zero for the other examined sleep variables. These findings were reproduced in the subgroup analyses that compared men and women, as well as patients with bipolar versus schizophrenia spectrum disorders. When excluding patients with extensive periods of wakefulness after the initial sleep period (wake after sleep onset > 100 minutes), the reliability of the actigraphy-derived sleep variables markedly improved.
  
  
  CONCLUSIONS
  Actigraphy reliably measures the total sleep time in this specific patient population. For patients without extensive periods of wakefulness after sleep onset, actigraphy might provide a useful measure of sleep efficiency, sleep latency, and number of awakenings.
authors.affiliation: Center for Neuropsychiatric Schizophrenia Research (CNSR), Copenhagen University Hospital, Mental Health Center Glostrup, Mental Health Services - Capital Region of Denmark, Glostrup, Denmark ; Center for Clinical Intervention and Neuropsychiatric Schizophrenia Research (CINS), Copenhagen University Hospital, Mental Health Center Glostrup, Mental Health Services - Capital Region of Denmark, Glostrup, Denmark.
authors.forename: Lone
authors.initials: L
authors.lastname: Baandrup
authors.affiliation: Danish Center for Sleep Medicine, Department of Clinical Neurophysiology, Center for Healthy Ageing, Faculty of Health Sciences, University of Copenhagen, Rigshospitalet, Glostrup, Denmark.
authors.forename: Poul Jørgen
authors.initials: PJ
authors.lastname: Jennum
keywords: actigraphy; bipolar disorder; polysomnography; schizophrenia; validation