title: Characterizing cognitive heterogeneity on the schizophrenia-bipolar disorder spectrum.
abstract: BACKGROUND
  Current group-average analysis suggests quantitative but not qualitative cognitive differences between schizophrenia (SZ) and bipolar disorder (BD). There is increasing recognition that cognitive within-group heterogeneity exists in both disorders, but it remains unclear as to whether between-group comparisons of performance in cognitive subgroups emerging from within each of these nosological categories uphold group-average findings. We addressed this by identifying cognitive subgroups in large samples of SZ and BD patients independently, and comparing their cognitive profiles. The utility of a cross-diagnostic clustering approach to understanding cognitive heterogeneity in these patients was also explored.
  
  
  METHODS
  Hierarchical clustering analyses were conducted using cognitive data from 1541 participants (SZ n = 564, BD n = 402, healthy control n = 575).
  
  
  RESULTS
  Three qualitatively and quantitatively similar clusters emerged within each clinical group: a severely impaired cluster, a mild-moderately impaired cluster and a relatively intact cognitive cluster. A cross-diagnostic clustering solution also resulted in three subgroups and was superior in reducing cognitive heterogeneity compared with disorder clustering independently.
  
  
  CONCLUSIONS
  Quantitative SZ-BD cognitive differences commonly seen using group averages did not hold when cognitive heterogeneity was factored into our sample. Members of each corresponding subgroup, irrespective of diagnosis, might be manifesting the outcome of differences in shared cognitive risk factors.
authors.affiliation: Melbourne Neuropsychiatry Centre,Department of Psychiatry,University of Melbourne and Melbourne Health,Carlton,VIC,Australia.
authors.forename: T E
authors.initials: TE
authors.lastname: Van Rheenen
authors.affiliation: Schizophrenia and Bipolar Disorder Program,McLean Hospital,Belmont, MA,USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Lewandowski
authors.affiliation: Brain and Psychological Sciences Research Centre,Faculty of Health, Arts and Design,School of Health Sciences, Swinburne University,Hawthorn,VIC,Australia.
authors.forename: E J
authors.initials: EJ
authors.lastname: Tan
authors.affiliation: Icahn School of Medicine,Mount Sinai, NY,USA.
authors.forename: L H
authors.initials: LH
authors.lastname: Ospina
authors.affiliation: Schizophrenia and Bipolar Disorder Program,McLean Hospital,Belmont, MA,USA.
authors.forename: D
authors.initials: D
authors.lastname: Ongur
authors.affiliation: Brain and Psychological Sciences Research Centre,Faculty of Health, Arts and Design,School of Health Sciences, Swinburne University,Hawthorn,VIC,Australia.
authors.forename: E
authors.initials: E
authors.lastname: Neill
authors.affiliation: Cognitive Neuropsychiatry Laboratory,Monash Alfred Psychiatry Research Centre, The Alfred Hospital and Central Clinical School, Monash University,Melbourne,VIC,Australia.
authors.forename: C
authors.initials: C
authors.lastname: Gurvich
authors.affiliation: Melbourne Neuropsychiatry Centre,Department of Psychiatry,University of Melbourne and Melbourne Health,Carlton,VIC,Australia.
authors.forename: C
authors.initials: C
authors.lastname: Pantelis
authors.affiliation: Hofstra Northwell School of Medicine,Hempstead, NY,USA.
authors.forename: A K
authors.initials: AK
authors.lastname: Malhotra
authors.affiliation: Brain and Psychological Sciences Research Centre,Faculty of Health, Arts and Design,School of Health Sciences, Swinburne University,Hawthorn,VIC,Australia.
authors.forename: S L
authors.initials: SL
authors.lastname: Rossell
authors.affiliation: Icahn School of Medicine,Mount Sinai, NY,USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Burdick
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000145:classification / Q000150:complications / Q000503:physiopathology; D060825:Cognitive Dysfunction / Q000145:classification / Q000209:etiology / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012559:Schizophrenia / Q000145:classification / Q000150:complications / Q000503:physiopathology; D055815:Young Adult
keywords: Clustering; cognition; heterogeneity; neuropsychology; psychosis spectrum