Mapping of the PDQ-39 to EQ-5D scores in patients with Parkinson's disease.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
School of Medicine, Population and Social Health Research Group, GHI, Griffith University, Logan Campus, University Drive, Meadowbrook, QLD, 4131, Australia. megan.young@griffith.edu.au
Megan K
MK
Young
Shu-Kay
SK
Ng
George
G
Mellick
Paul A
PA
Scuffham
D000203:Activities of Daily Living / Q000523:psychology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D005260:Female; D006304:Health Status; D006801:Humans; D007802:Language; D016014:Linear Models; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D010300:Parkinson Disease / Q000175:diagnosis / Q000523:psychology*; D011594:Psychometrics / Q000295:instrumentation*; D011788:Quality of Life; D015203:Reproducibility of Results; D012648:Self Care / Q000523:psychology; D018434:Sickness Impact Profile; D012944:Social Support; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires / Q000592:standards*