Table 2. Period frequency^a of persistent drug-induced movement disorder^b in 194 patients, by tertile age group.

	Age (years)c
Movement disorder (%)	≤40 (n = 65)	41–52 (n = 65)	≥53 (n = 64)	zc	p
Tardive dyskinesia (n = 55)	15.4	32.3	37.5	2.78	0.005
Parkinsonism (n = 109)	40.0	49.2	79.7	4.52	0.000
Akathisia (n = 9)	7.7	6.2	0.0	−2.07	0.039
Tardive dystonia (n = 11)	1.5	6.2	9.4	1.92	0.055

^aMean period was 1.1 year (SD 0.6).

^bPersistent movement disorder: 2 consecutive positive assessments with an interval of at least 3 months.

^cNonparametric test for trend across ordered groups (extension of the Wilcoxon rank-sum test).