Rasch analysis of the carers quality of life questionnaire for parkinsonism.

OBJECTIVE: To assess the psychometric properties of the Carers Quality of Life Questionnaire for Parkinsonism using a Rasch modeling approach and determine the optimal cut-off score. METHODS: We performed a Rasch analysis of the survey answers of 430 carers of patients with atypical parkinsonism. RESULTS: All of the scale items demonstrated acceptable goodness of fit to the Rasch model. The scale was unidimensional and no notable differential item functioning was detected in the items regarding age and disease type. Rating categories were functioning adequately in all scale items. The scale had high reliability (.95) and construct validity and a high degree of precision, distinguishing between 5 distinct groups of carers with different levels of quality of life. A cut-off score of 62 was found to have the optimal screening accuracy based on Hospital Anxiety and Depression Scale subscores. CONCLUSION: The results suggest that the Carers Quality of Life Questionnaire for Parkinsonism is a useful scale to assess carers' quality of life and allows analyses requiring interval scaling of variables. © 2016 International Parkinson and Movement Disorder Society.

Development and validation of a carers quality-of-life questionnaire for parkinsonism (PQoL Carers).

PURPOSE: Atypical parkinsonism (AP) has a considerable impact on the lives not only of patients but also of their carers. The aim of this study was to develop an instrument for assessing the quality of life (QoL) of carers of patients with AP. METHODS: A 40-item pool was generated from in-depth interviews with carers of patients with AP, a thorough review of the existing literature and consultation with movement disorder experts. Item refinement and reduction was performed using the results of pilot testing and a survey in 282 carers of multiple system atrophy (MSA) patients and 226 carers of progressive supranuclear palsy (PSP) patients. A validation study, with responses of 243 carers of MSA and 187 carers of PSP patients, was undertaken to evaluate the psychometric properties of the final 26-item scale. RESULTS: The validation study results suggest that the scale is unidimensional and has high internal consistency (Cronbach's α = 0.96). The correlations of scale scores with patients' health status and QoL measures, such as PDQ-39 summary score and EQ-5D index (Spearman's ρ = 0.56 and -0.31, respectively, P < 0.001), as well as carers' measures, such as Caregiver Burden Inventory (CBI) total and EQ-5D index (Spearman's ρ = 0.85 and -0.39, respectively, P < 0.001), document the convergent and concurrent validity of the scale. ANOVA results support the discriminant validity of the scale, as evidenced by its capacity to differentiate between carers with varying levels of self-reported health. CONCLUSIONS: The 26-item Parkinsonism Carers QoL (PQoL Carer) is a concise instrument with adequate psychometric qualities that can be used for clinical and research purposes.