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Assessing the Validity and Reliability of the International Anxiety and Depression Questionnaire in Two Bereaved National Samples

Philip Hyland1*, Enya Redican2, Thanos Karatzias3, Mark Shevlin2

Background: The International Anxiety Questionnaire (IAQ) and International Depression Questionnaire (IDQ) have been developed as self-report measures of ICD-11 Generalized Anxiety Disorder (ICD-11 GAD) and ICD-11 Single Episode Depressive Disorder (ICD-11 DD). This study tested the psychometric properties of the IAQ and IDQ in two samples of bereaved adults from the United Kingdom (UK) and the Republic of Ireland.

Objective: Confirmatory Factor Analysis (CFA) was used to test the combined dimensionality and measurement invariance of the IAQ and IDQ across the UK (n=1,012) and Irish (n=1,011) samples. Differential item functioning was tested using Multiple Indicator Multiple Cause (MIMIC) modelling based on country, age, and sex while convergent validity was assessed using bivariate correlations. Prevalence rates of ICD-11 GAD and ICD-11 DD were also estimated.

Results: The CFA results supported a correlated two-factor model in both samples. The UK had higher latent variable means for depression and anxiety, older adults had lower latent variable means for depression and anxiety, and females had higher latent variable means for anxiety. The MIMIC model showed that the IDQ item "Had recurrent thoughts of death or suicide" showed DIF and the effect was small. Internal reliability of the scales was high while scores on the IAQ and IDQ were highly correlated with scores on external measures of anxiety, depression, and prolonged grief disorder. The IAQ and IDQ effectively distinguished between individuals with and without a history of mental health treatment. The prevalence of ICD-11 GAD was 18.6% and 16.1% and ICD-11 DD was 13.8% and 10.5% in the UK and Irish samples, respectively.

Conclusion: Findings of the study provide support for the validity, measurement invariance, and reliability of the IAQ and IDQ among two bereaved national samples.