Dementia Caregiving: the construct validity of the CarerQol instrument to measure the impact of informal care among caregivers of dementia patients.

Objectives: In recent years, informal care is not systematically included in economic evaluations, while this could lead to suboptimal decision making. The impact of caregiving on carers is often substantial and most of the times negative, especially when the care recipients suffer from mental illnesses such as dementia. Thus, valid and reliable instruments are required to measure these carer effects for inclusion in economic assessments. This study investigates the construct validity of the Care-related Quality of Life (CarerQol)-instrument among informal caregivers of Dementia patients. The CarerQol instrument measures and values the impact of informal care by assessing happiness (CarerQol-VAS) and describing burden dimensions (CarerQol-7D). Methods: The data were gathered with written questionnaires distributed by post in a population of informal caregivers of dementia patients living at home in the Gooi and Vechtstreek region (near Amsterdam) (n = 602, net response rate = 37%). Two different types of construct validity, i.e. convergent and clinical validity have been assessed. Convergent validity was analyzed with assessing Spearman’s correlation coefficients and multivariate correlation between the burden dimensions (CarerQol-7D) and the valuation component (CarerQol-VAS) of the CarerQol. Additionally, the convergent validity was tested with Spearman’s correlation coefficients between CarerQol and other subjective burden measures (SRB, CSI, Pt). Further, the convergent validity was evaluated with multivariate correlation between CarerQol-VAS and CarerQol-7D among subgroups of caregivers. The clinical validity was assessed with multivariate correlation between CarerQol-VAS and CarerQol-7D, characteristics of caregivers, care recipients and care situation. Additionally, exploratory analysis was performed concerning the convergent and clinical validity of the recently developed valuation component of CarerQol, the CarerQol-7D sum score (CarerQol-7D Tariff) in a similar way. Results: The negative/positive dimensions of CarerQol-7D were negatively/positively related to CarerQol-VAS, and most of them had moderate strength of convergent validity. The CarerQol-VAS was negatively associated with SRB and CSI and positively with Pt. The CarerQol-VAS reflected differences in important background characteristics: educational level and subjective health of the caregiver, intensity of caregiving (in number of days per week) and use of professional home care. Our results largely corroborated earlier tests of the construct validity of the CarerQol. Additionally, the CarerQol-7D dimensions significantly explained differences in CarerQol-VAS scores among subgroups of caregivers. The exploratory analysis concerning the construct validity of the CarerQol-7D sum score showed that the latter was negatively associated with SRB and CSI and positively with CarerQol-VAS and Pt. Moreover, CarerQol-7D sum score reflected differences in certain background characteristics of the caregivers, care recipients and care situation which all together explained 35% of the variation in the CarerQol-7D sum scores. Conclusion: Notwithstanding the study limitations such as the selective and of modest size sample of caregivers, this study suggests that the CarerQol is a valid tool to measure and value the impact of informal care among these special providers of care for use in economic evaluations.