title: Approximate entropy as a measure of irregularity for psychiatric serial metrics.
abstract: OBJECTIVE
  The quantification of subtle patterns in sequential data, and their changes, has considerable potential utility throughout psychiatry, including the analyses of mood ratings, heart rate, respiratory, and electroencephalographic recordings.
  
  
  METHODS
  Approximate entropy (ApEn), a relatively recently developed statistic quantifying serial irregularity, has been applied in numerous studies throughout mathematics and other fields of study, especially biology.
  
  
  RESULTS
  We discussed applications of ApEn, both extant and potential, of most relevance to psychiatrists. We provided a mechanistic interpretation of lowered ApEn values, and discusses the relationship between ApEn and other (both classical and complexity) measures of serial dynamics. We also briefly discussed cross-ApEn, a thematically similar quantification of two-variable asynchrony that can aid in uncovering subtle disruptions in complicated network dynamics.
  
  
  CONCLUSIONS
  ApEn and cross-ApEn have significant potential to consequentially enhance present statistical methodologies of analysis of psychiatric data, in both clinical and in research settings.
authors.affiliation: stevepincus@alum.mit.edu
authors.forename: Steven M
authors.initials: SM
authors.lastname: Pincus
mesh_terms: D000328:Adult; D000339:Affect / Q000502:physiology; D000368:Aged; D001143:Arousal / Q000502:physiology; D001683:Biological Clocks / Q000502:physiology; D001714:Bipolar Disorder / Q000175:diagnosis / Q000503:physiopathology / Q000523:psychology*; D003625:Data Collection / Q000706:statistics & numerical data; D004569:Electroencephalography / Q000706:statistics & numerical data; D019277:Entropy; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D011594:Psychometrics / Q000706:statistics & numerical data*; D013739:Testosterone / Q000097:blood
chemical_list: D013739:Testosterone; D007986:Luteinizing Hormone