Assessing the impact on caregivers of patients with schizophrenia: psychometric validation of the Schizophrenia Caregiver Questionnaire (SCQ)

Abstract

Background: The Schizophrenia Caregiver Questionnaire (SCQ) was developed to assess the impact on caregivers of caring for patients with schizophrenia. The objective of this study was to develop a scoring algorithm for the SCQ, and evaluate its measurement properties.

Methods: The SCQ was administered to 358 caregivers of patients with schizophrenia included in the observational PATTERN study of stabilized patients with persistent symptoms of schizophrenia receiving outpatient care. SCQ item selection and creation of scores were based on exploration of item response distribution, factor analyses, and Rasch model. Construct validity, reliability, and ability to detect change of the SCQ scores were investigated.

Results: The final questionnaire comprised a 'Humanistic impact' supra-domain composed of a global score and four subdomain scores ('Physical'; 'Emotional'; 'Social'; 'Daily life'), and eight other domain scores related to the caregiving role ('Exhaustion with caregiving'; 'Feeling alone'; 'Patient Dependence'; 'Worries for the patient'; 'Perception of caregiving'; 'Financial dependence of the patient'; 'Financial impact of caregiving'; 'Overall difficulty of caregiving'). Two items from the SCQ were deleted. SCQ scores showed very good construct validity: Item convergent/discriminant validity were satisfactory; SCQ scores of caregivers of patients with more severe symptoms were higher indicating more impact (p < 0.05 for all scores); SCQ scores were meaningfully associated with measures of schizophrenia severity (PANSS and PSP) and caregivers' Health-Related Quality of Life (Medical Outcome Survey Short Form 36 items). The SCQ Humanistic impact supra-domain scores demonstrated very good internal consistency reliability (Cronbach's alphas between 0.80 and 0.96) and test-retest reliability (Intraclass Coefficient correlations ranging from 0.75 and 0.87); Other SCQ domain scores showed lower but still acceptable reliability coefficients. SCQ scores clearly increased for caregivers of patients whose schizophrenia worsened.

Conclusions: Overall, the 30-item SCQ demonstrated very good measurement properties supporting its relevance to comprehensively measure the experience of caregivers of patients with schizophrenia.

Keywords: Caregiver; Impact; Quality of life; Questionnaires; Schizophrenia; Validation.

Fig. 1

CFA results of the final model of the SCQ linking items, concepts, and the total “Humanistic impact” at baseline in the caregiver analysis set (N = 358); RMSEA: Root Mean Square Error of Approximation; SRMR: Standard Root Mean square Residuals; GFI: Goodness of Fit Index; AGFI: Adjusted Goodness of Fit Index; NFI: Normed Fixed Index; CFI: Comparative Fit Index

Fig. 2

Person-item distribution of SCQ items of the Humanistic impact from the Rating Scale Model with items scored with 5 categories at baseline (N = 358)

Fig. 3

Measurement properties of SCQ: a Clinical validity - comparison of the SCQ domain scores according to CaGI-S at baseline in the caregiver analysis set (N = 358); b Ability to detect change - comparison of the change in SCQ domain scores according to CaGI-I between baseline and 6 months in patients with SCQ data at baseline and Month 6 (N = 270)