title: Comparison of a Commercial Accelerometer with Polysomnography and Actigraphy in Children and Adolescents.
abstract: OBJECTIVE
  To evaluate the reliability and validity of the commercially available Fitbit Ultra (2012) accelerometer compared to polysomnography (PSG) and two different actigraphs in a pediatric sample.
  
  
  METHODS
  All subjects wore the Fitbit Ultra while undergoing overnight clinical polysomnography in a sleep laboratory; a randomly selected subset of participants also wore either the Ambulatory Monitoring Inc. Motionlogger Sleep Watch (AMI) or Phillips-Respironics Mini-Mitter Spectrum (PRMM).
  
  
  METHODS
  63 youth (32 females, 31 males), ages 3-17 years (mean 9.7 years, SD 4.6 years).
  
  
  METHODS
  Both "Normal" and "Sensitive" sleep-recording Fitbit Ultra modes were examined. Outcome variables included total sleep time (TST), wake after sleep onset (WASO), and sleep efficiency (SE). Primary analyses examined the differences between Fitbit Ultra and PSG using repeated-measures ANCOVA, with epoch-by-epoch comparisons between Fitbit Ultra and PSG used to determine sensitivity, specificity, and accuracy. Intra-device reliability, differences between Fitbit Ultra and actigraphy, and differences by both developmental age group and sleep disordered breathing (SDB) status were also examined.
  
  
  RESULTS
  Compared to PSG, the Normal Fitbit Ultra mode demonstrated good sensitivity (0.86) and accuracy (0.84), but poor specificity (0.52); conversely, the Sensitive Fitbit Ultra mode demonstrated adequate specificity (0.79), but inadequate sensitivity (0.70) and accuracy (0.71). Compared to PSG, the Fitbit Ultra significantly overestimated TST (41 min) and SE (8%) in Normal mode, and underestimated TST (105 min) and SE (21%) in Sensitive mode. Similar differences were found between Fitbit Ultra (both modes) and both brands of actigraphs.
  
  
  CONCLUSIONS
  Despite its low cost and ease of use for consumers, neither sleep-recording mode of the Fitbit Ultra accelerometer provided clinically comparable results to PSG. Further, pediatric sleep researchers and clinicians should be cautious about substituting these devices for validated actigraphs, with a significant risk of either overestimating or underestimating outcome data including total sleep time and sleep efficiency.
authors.affiliation: National Jewish Health, Denver, CO.
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Meltzer
authors.affiliation: University at Albany, State University of New York, Albany, NY.
authors.forename: Laura S
authors.initials: LS
authors.lastname: Hiruma
authors.affiliation: University of Alabama at Birmingham, Birmingham, AL.
authors.forename: Kristin
authors.initials: K
authors.lastname: Avis
authors.affiliation: West Virginia University, Morgantown, WV.
authors.forename: Hawley
authors.initials: H
authors.lastname: Montgomery-Downs
authors.affiliation: Children's of Alabama, Birmingham, AL.
authors.forename: Judith
authors.initials: J
authors.lastname: Valentin
mesh_terms: D061725:Accelerometry / Q000191:economics / Q000295:instrumentation*; D056044:Actigraphy / Q000295:instrumentation; D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D003365:Costs and Cost Analysis; D005260:Female; D006801:Humans; D008297:Male; D017286:Polysomnography; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012890:Sleep / Q000502:physiology*; D012891:Sleep Apnea Syndromes / Q000503:physiopathology; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology
keywords: Fitbit; accelerometer; actigraphy; pediatric; polysomnography; sensitivity; specificity; validation