PD Case definitions

For analysis purposes, PD cases were determined using a combination of responses to survey questions and a physician diagnosis (self-reported):

Definitive PD: Responses to survey questions indicative of PD AND a PD diagnosis was provided by the participant’s physician.

Probable PD: Responses to survey questions indicative of PD BUT NO PD diagnosis provided by the participant’s physician.

No PD: Responses to survey questions not indicative of PD and no PD diagnosis provided by the participant’s physician.

When comparing with survey participants who were classified as ‘No PD’ cases, the two classifications of PD cases were combined into one level (Definitive/Probable).

For categorical variables, analyses and comparisons were performed using chi-square methods. Bonferroni corrections were used when multiple comparisons were performed, resulting in the α level being reduced to α/n. For all other analyses, a p-value <0.05 was considered statistically significant. Parametric (t-test and ANOVA) methods were used to compare continuous variables as needed and appropriate. The associations between various survey factors and PD status (Probable/Definitive PD vs No PD) were assessed.

Univariate and multivariable (stepwise) logistic regression models were used to generate Odds Ratios (with 95% CI) of PD status using various demographic characteristics as independent predictors. All statistical analyses were performed using SAS 9.3 (SAS Institute, Cary NC).