Study population

Sample size was based primarily on feasibility since no formal hypothesis was tested in this study. A target of 450 patients with advanced-stage PD were to be recruited under the assumption of a 60% prevalence of ND in populations with PD, providing a precision of 4.5% in prevalence estimate.

Inclusion criteria for the study were ≥ 30 years of age, diagnosed with idiopathic PD according to the UK Parkinson’s Disease Society Brain Bank criteria, Stage II to IV of the Modified H&Y scale, wearing off (motor fluctuations) despite optimized pharmacological treatment (levodopa monotherapy or adjunctive therapies), history of ≥3 h awake “off” time per day for the past 4 weeks based on the investigator’s knowledge of the patient, able to comprehend Mandarin Chinese, and provide written informed consent. Exclusion criteria were clinical diagnosis of dementia, atypical Parkinsonism, unable to complete interviews as assessed by investigators, unable to complete the PDSS-2 and PDQ-39 with the support of the investigator, or currently participating in any PD clinical studies testing interventional drugs or disease management programs.