Joseph Chilcot1, Joanna L Hudson2, Rona Moss-Morris2, Amy Carroll3, David Game3, Anna Simpson4, Matthew Hotopf4. 1. Health Psychology Section, Psychology Department, Institute of Psychiatry, Psychology and Neuroscience, King's College London, UK. Electronic address: joseph.chilcot@kcl.ac.uk. 2. Health Psychology Section, Psychology Department, Institute of Psychiatry, Psychology and Neuroscience, King's College London, UK. 3. Guy's and St Thomas' NHS Foundation Trust, UK. 4. Department of Psychological Medicine, Institute of Psychiatry, Psychology, and Neuroscience, King's College London, UK.
Abstract
OBJECTIVE: To validate the factor structure of the Patient Health Questionnaire Anxiety and Depression Scale (PHQ-ADS)- which is a composite measure of depression and anxiety using the Patient Health Questionnaire-9 and Generalised Anxiety Disorder Scale (GAD-7), in a sample of haemodialysis patients. METHOD: Screening data (n=182) used to select entry into a feasibility study of an online cognitive-behavioural therapy intervention for distress in dialysis patients were analysed here. Structural validity of the PHQ-ADS was evaluated using confirmatory factor analysis (CFA), assessing alternative models including a bi-factor model. In the bi-factor model all items from the PHQ-9 and GAD-7 (16-items in total) were loaded onto a general distress factor. Respective items of the PHQ-9 and GAD-7 were specified as subgroup factors. Omega-hierarchical was calculated to indicate the level of saturation of a multidimensional scale by a general factor. Construct validity was determined against the Brief Illness Perception Questionnaire. RESULTS: A bi-factor PHQ-ADS model had good fit to the data (chi-square=96.1, p=0.26, CFI=0.99; TLI=0.99; RMSEA=0.02). The general distress factor accounted for approximately 84% of the explained variance (omega-h=0.90). Distress scores were significantly higher in females compare with males. There was a significant association between distress and negative illness perceptions (r=0.58, p<0.01). CONCLUSIONS: The PHQ-ADS appears to have good structural validity in haemodialysis patients and is sufficiently unidimensional to warrant the use of a total distress score. A full psychometric analysis of the PHQ-ADS in a larger sample of dialysis patients is warranted.
OBJECTIVE: To validate the factor structure of the Patient Health Questionnaire Anxiety and Depression Scale (PHQ-ADS)- which is a composite measure of depression and anxiety using the Patient Health Questionnaire-9 and Generalised Anxiety Disorder Scale (GAD-7), in a sample of haemodialysis patients. METHOD: Screening data (n=182) used to select entry into a feasibility study of an online cognitive-behavioural therapy intervention for distress in dialysis patients were analysed here. Structural validity of the PHQ-ADS was evaluated using confirmatory factor analysis (CFA), assessing alternative models including a bi-factor model. In the bi-factor model all items from the PHQ-9 and GAD-7 (16-items in total) were loaded onto a general distress factor. Respective items of the PHQ-9 and GAD-7 were specified as subgroup factors. Omega-hierarchical was calculated to indicate the level of saturation of a multidimensional scale by a general factor. Construct validity was determined against the Brief Illness Perception Questionnaire. RESULTS: A bi-factor PHQ-ADS model had good fit to the data (chi-square=96.1, p=0.26, CFI=0.99; TLI=0.99; RMSEA=0.02). The general distress factor accounted for approximately 84% of the explained variance (omega-h=0.90). Distress scores were significantly higher in females compare with males. There was a significant association between distress and negative illness perceptions (r=0.58, p<0.01). CONCLUSIONS: The PHQ-ADS appears to have good structural validity in haemodialysis patients and is sufficiently unidimensional to warrant the use of a total distress score. A full psychometric analysis of the PHQ-ADS in a larger sample of dialysis patients is warranted.
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