Mapping of the PDQ-39 to EQ-5D scores in patients with Parkinson’s disease
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The EuroQoL (EQ-5D) is ideal to compare quality of life across conditions. However, the Parkinson’s Disease Questionnaire (PDQ-39) is often the only quality-of-life instrument used in Parkinson’s disease research. We aimed to identify associations between PDQ-39 domains and EQ-5D domains, and compare different methods of developing a function to map the PDQ-39 to EQ-5D scores.
Adults with Parkinson’s disease self-completed both instruments. Ordinal regression identified associations between PDQ-39 domain scores and each EQ-5D domain. Modeling (n = 80) and validation sets (n = 16) were randomly generated. Overall performance of four methods of mapping the PDQ-39 to EQ-5D scores (using PDQ-39 domains and total score in ordinal and linear regression) was assessed with the validation set, followed by assessing the equivalence of observed and predicted EQ-5D scores on the full dataset controlling for sociodemographic factors.
Different sets of PDQ-39 domains were associated with each EQ-5D domain. For example, PDQ-39 “Activities of Daily Living” and “Social Support” were associated with EQ-5D “Personal Care,” while PDQ-39 “Emotional Well-being” was associated with EQ-5D “Anxiety/Depression.” Over one-third (37.5 %) of predictions from ordinal regressions had an error <0.01 % (compared to 6.3 % for linear regressions). The EQ-5D scores predicted with ordinal regression using PDQ-39 domains were similar in distribution and association with sociodemographic factors to the observed EQ-5D scores.
Of the four methods tested, using PDQ-39 domains in ordinal regression was superior for mapping EQ-5D scores. The function reported here may prove particularly useful for cost-utility analyses comparing Parkinson’s disease with other conditions.
KeywordsQuality of life PDQ-39 EQ-5D Parkinson’s disease Economic evaluation
Censored least absolute deviations
Deep brain stimulation
EuroQoL utility index
Mean absolute deviation
Missing at random
Missing completely at random
Ordinary least squares
Parkinson’s Disease Questionnaire
Queensland Parkinson’s disease Project
Root mean squared error
Statistical Package for the Social Sciences
Visual analogue scale
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