title: Differential reporting of depressive symptoms across distinct clinical subpopulations: what DIFference does it make?
abstract: OBJECTIVE
  To investigate the impact of differences in depressive symptom reporting across clinical groups (healthcare setting, chronic illness, depression diagnosis and anxiety diagnosis) on clinical interpretability and comparability of depression scores.
  
  
  METHODS
  Participants from the Netherlands Study of Depression and Anxiety (n=2981) completed the self-report Inventory of Depressive Symptomatology (IDS-SR). Differences in depressive symptom reporting between distinct clinical subpopulations were assessed using a Differential Item Functioning (DIF) analysis. The effects of DIF on symptom level were evaluated by examining whether DIF-adjustment had clinically relevant effects.
  
  
  RESULTS
  Significant DIF was detected across all tested clinical subpopulation groupings. Clinically relevant DIF was found on the symptom level for 13 IDS-SR items. However, impact of DIF on the aggregate level ranged from small to negligible: adjustment for DIF only led to salient changes in aggregate scores for 0.2-12.7% of individuals across tested sources of DIF.
  
  
  CONCLUSIONS
  Differences in endorsement patterns of depressive symptoms were observed across clinical populations, challenging the assumptions regarding the measurement properties of self-reported depression. However, effects of DIF on the aggregate level of IDS-SR total scores were found to be minimal and not clinically important. The IDS-SR thus seems robust against DIF across clinical populations.
authors.affiliation: University of Groningen, University Medical Center Groningen, Interdisciplinary Center Psychopathology and Emotion regulation (ICPE), Groningen, The Netherlands. Electronic address: r.b.k.wanders@umcg.nl.
authors.forename: Rob B K
authors.initials: RB
authors.lastname: Wanders
authors.affiliation: University of Groningen, University Medical Center Groningen, Interdisciplinary Center Psychopathology and Emotion regulation (ICPE), Groningen, The Netherlands.
authors.forename: Klaas J
authors.initials: KJ
authors.lastname: Wardenaar
authors.affiliation: Department of Health Care Policy, Harvard Medical School, Boston, MA, United States.
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Kessler
authors.affiliation: Department of Psychiatry and EMGO Institute for Health and Care Research, VU University Medical Centre, Amsterdam, the Netherlands.
authors.forename: Brenda W J H
authors.initials: BW
authors.lastname: Penninx
authors.affiliation: University of Groningen, Department of Psychometrics and Statistics, The Netherlands.
authors.forename: Rob R
authors.initials: RR
authors.lastname: Meijer
authors.affiliation: University of Groningen, University Medical Center Groningen, Interdisciplinary Center Psychopathology and Emotion regulation (ICPE), Groningen, The Netherlands.
authors.forename: Peter
authors.initials: P
authors.lastname: de Jonge
mesh_terms: D000328:Adult; D001007:Anxiety / Q000175:diagnosis* / Q000453:epidemiology*; D001008:Anxiety Disorders / Q000175:diagnosis; D003863:Depression / Q000175:diagnosis* / Q000453:epidemiology*; D003866:Depressive Disorder / Q000175:diagnosis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D010555:Personality Inventory; D057566:Self Report; D012917:Social Adjustment
keywords: Depression; Differential item functioning; IDS-SR; Item response theory; Measurement