Measurement invariance of the Patient Health Questionnaire (PHQ-9) and Generalized Anxiety Disorder scale (GAD-7) across four European countries during the COVID-19 pandemic

M Shevlin, Sarah Butter, Orla McBride, Jamie Murphy, Jilly Gibson‐Miller, Todd K. Hartman, Liat Levita, Liam Mason, Anton P. Martinez, Ryan McKay, Thomas VA Stocks, Kate M. Bennett, Philip Hyland, Frédérique Vallieres, Carmen Valiente, Carmelo Vazquez, Alba Contreras, Vanesa Peinado, Almudena Trucharte, Marco BertaminiAnna Panzeri, Giovanni Bruno, Umberto Granziol, Giuseppe Mignemi, Andrea Spoto, Giulio Vidotto, Richard P. Bentall

Research output: Contribution to journalArticlepeer-review

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Background: The Patient Health Questionnaire (PHQ-9) and Generalized Anxiety Disorder scale (GAD-7) are self-report measures of major depressive disorder and generalised anxiety disorder. The primary aim of this study was to test for differential item functioning (DIF) on the PHQ-9 and GAD-7 items based on age, sex (males and females), and country.
Method: Data from nationally representative surveys in UK, Ireland, Spain, and Italy (combined N = 6,054) were used to fit confirmatory factor analytic and multiple-indictor multiple-causes models.
Results: Spain and Italy had higher latent variable means than the UK and Ireland for both anxiety and depression, but there was no evidence for differential items functioning.
Conclusions: The PHQ-9 and GAD-7 scores were found to be unidimensional, reliable, and largely free of DIF in data from four large nationally representative samples of the general population in the UK, Ireland, Italy and Spain.
Original languageEnglish
Article number154
JournalBMC Psychiatry
Issue number1
Early online date1 Mar 2022
Publication statusPublished online - 1 Mar 2022

Bibliographical note

Funding Information:
Ireland: The Irish strand of this study was funded by the Health Research Board and the Irish Research Council under the COVID-19 Pandemic Rapid Response Funding Call [COV19-2020-025] awarded to PH.

Funding Information:
UK: The initial stages of this project were supported by start-up funds from the University of Sheffield (Department of Psychology, the Sheffield Methods Institute and the Higher Education Innovation Fund via an Impact Acceleration grant administered by the university) and by the Faculty of Life and Health Sciences at Ulster University. The research was subsequently supported by UK Research and Innovation/Economic and Social Research Council funding (grant ref. ES/V004379/1) and awarded to RPB, TKH, LL, JGM, MS, JM, OM, KB and LM.

Funding Information:
Spain: This research was supported by grants from the Ministry of Science and Innovation (PSI2016-74987-P) and Instituto de Salud Carlos III (COV20/00737) to Carmen Valiente and funds from the UCM for consolidated research groups (GR29/20) to Carmelo Vazquez.

Funding Information:
Italy: This research was funded by the University “La Sapienza” of Roma and the Department of General Psychology of the University of Padua.

Publisher Copyright:
© 2022, The Author(s).


  • Anxiety
  • Depression
  • GAD-7
  • Measurement invariance
  • PHQ-9
  • Pandemics
  • Patient Health Questionnaire
  • Humans
  • Male
  • Psychometrics
  • SARS-CoV-2
  • COVID-19/epidemiology
  • Female
  • Surveys and Questionnaires
  • Depressive Disorder, Major/diagnosis
  • Measurement Invariance
  • Gad-7
  • COVID-19
  • Depressive Disorder, Major
  • Phq-9


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