TABLE 1.

Discrimination parameters of all MDS‐UPDRS Part III items from fitting 2 IRT models to 23 nontremor items and 10 tremor items separately based on the on and off states

Item number	Source of information	On State		Off State
		Nontremor	Tremor	Nontremor	Tremor
3.1	Speech	1.459		1.380
3.2	Facial expression	1.528		1.591
3.3a	Rigidity–neck	1.405		1.538
3.3b	Rigidity–RUE	1.345		1.575
3.3c	Rigidity–LUE	1.447		1.591
3.3d	Rigidity–RLE	1.573		1.729
3.3e	Rigidity–LLE	1.608		1.879
3.4a	Finger tapping–right hand	2.024		2.025
3.4b	Finger tapping–left hand	2.173		2.376
3.5a	Hand movements–right hand	2.293		2.340
3.5b	Hand movements–left hand	2.251		2.341
3.6a	Pronation–supination–right hand	2.109		2.062
3.6b	Pronation–supination–left hand	2.095		2.207
3.7a	Toe tapping–right foot	2.018		2.573
3.7b	Toe tapping–left foot	2.010		2.737
3.8a	Leg agility–right leg	2.302		2.725
3.8b	Leg agility–left leg	2.376		2.973
3.9	Arising from chair	1.797		2.054
3.10	Gait	1.792		2.286
3.11	Freezing of gait	1.395		1.655
3.12	Postural stability	1.511		1.896
3.13	Posture	1.642		1.947
3.14	Global spontaneity of movement	2.095		2.497
3.15a	Postural tremor–right hand		2.238		2.215
3.15b	Postural tremor–left hand		2.041		2.140
3.16a	Kinetic tremor–right hand		1.919		1.910
3.16b	Kinetic tremor–left hand		1.661		1.842
3.17a	Rest tremor amplitude–RUE		2.634		2.571
3.17b	Rest tremor amplitude–LUE		2.648		2.514
3.17c	Rest tremor amplitude–RLE		2.267		2.059
3.17d	Rest tremor amplitude–LLE		2.213		2.295
3.17e	Rest tremor amplitude–lip/jaw		1.901		2.107
3.18	Constancy of rest tremor		3.017		2.508

On state = 6218 patients with visits measured in the on state; off state = 1745 patients with visits measured in the off state.

Abbreviations: MDS‐UPDRS, Movement Disorder Society Unified Parkinson's Disease Rating Scale; IRT, item response theory; RUE, right upper extremity; LUE, left upper extremity; RLE, right lower extremity; LLE, left lower extremity.