Table 3.

Study populations and case ascertainment methods

Study	Honolulu-Asia Aging Study	Ontario, Canada	Kaiser Permanente Northern California	Rochester Epidemiology Project	California PD registry project	US Medicare
Base population	8006 Japanese-American men born 1900–1919, living in Honolulu county, Hawaii, USA at baseline in 1965 and participating in the longitudinal Honolulu Heart Program	Residents of Ontario, Canada; all are provided health care paid for by the provincial government	Members of the Kaiser Permanente Northern California, a closed integrated health-care delivery system providing health insurance and health care to 25–30% of the population of Northern Californiaa	Residents of Olmsted county, Minnesota, USA	Residents of Kern, Tulare, Fresno, Santa Clara counties, California, USA	Residents of USA aged ≥65 years who use Medicare as their health-care insurer and whose insurance claims are released to Medicareb
Ascertainment method(s)/data source	Pre-1991: Hospitalization records, outpatient medical records, Post-1991: Screening in-person exam by trained research technician, positive cases examined by neurologist	Ontario Health-care administrative databases recording all inpatient and outpatient physician encounters	Medical record ascertainment that combined inpatient and outpatient diagnostic, pharmacy, treatment, and physician type15	Electronic screening for 53 H-ICDA codes for PD, parkinsonism, tremor, PSP, MSA, other extrapyramidal syndromes, non-specific neuro-degenerative diseases, followed by manual medical record review by neurologist28	Neurologists and large group practices asked to report all patients with ICD-9 code of PD (332) or other parkinsonism (332.1, 333.0, or 331.82). Trained abstractors manually extracted relevant elements of medical record	Medicare administrative claims database
Diagnostic criteria	Consensus diagnosis by movement disorders experts using hospitalization, outpatient neurologist records, and additionally after 1991 study screening examination and study neurologist’s standardized examination and Ward and Gibb criteria29	One hospitalization record or two outpatient visits with an assigned ICD diagnosis of PD (332 or G20) in the administrative record30	Algorithm that combines number of PD diagnoses, expertise of the physician making the diagnoses, and treatment	The presence of two of four cardinal signs: resting tremor, bradykinesia, rigidity, and impaired postural reflexes, without a known secondary cause, documented levodopa unresponsiveness or other atypical features28	ICD-9 code for PD (332). If more than one parkinsonism code was reported, manual medical record review by a movement disorder neurologist (CMT) to assign the most likely diagnosis	One ICD code for PD (332.0) and no atypical or secondary parkinsonism codes
Case definition validation method(s), if any	None	Medical record review. Sensitivity 72%, specificity 99%30	None	Clinicopathologic concordance 87% in 60 individuals31	A minimum of 10% validation using standardized chart abstraction protocol	None

H-ICDA Hospital adaptation of ICD. 53 H-ICDA diagnostic codes: 7 codes for PD, 12 for parkinsonism, 10 for tremor, 8 for other extrapyramidal symptoms, 6 for nonspecific neurodegenerative diseases, 5 for multiple system atrophy, and 5 for progressive supranuclear palsy

^aMembers are representative of the population of Northern California with respect to age, sex, and race/ethnicity and slightly less likely to have very low or very high income²⁷

^bWhile Medicare provides health insurance to 98% of the population aged ≥65 years, some individuals choose third-party medical insurance coverage and some health-care organizations or reimbursement programs do not release their claims data to Medicare due to privacy regulations or for other reasons