BOX 1.

Interpreting Individual PDAQ theta (ability) scores - In order to provide context regarding interpretation of ability scores generated by the IRT model for representative patients, thetas are provided along with measures of motor, cognitive, and functional impairment.

PD patient's cognitive status	Theta	MDRS-2	UPDRS-III	ADCS-ADL	DAFS
Patient 1 (intact)	1.68	138	23	78	53
Patient 2 (MCI)	0.47	134	22	77	52
Patient 3 (mild dementia)	–0.54	113	28	49	25
Patient 4 (severe dementia)	–1.65	101	37	17	1

Higher scores on the UPDRS-III indicate greater motor impairment. Lower scores on the MDRS-2, ADCS-ADL, and DAFS indicate greater cognitive and functional impairment, respectively.