Table 1. Comparison of behavioral results for the Erickson flanker tests between heroin-dependent patients and controls.

	heroin- dependent patients (n=20)	controls (n=15)	statistic	p
% non-response, median (IQR)	4.0 (1.3-11.4)	4.6 (2.0-5.8)	Z^a=0.13	0.894
% errors, median (IQR)	9.8 (4.9-28.1)	8.5 (6.8-11.8)	Z^a=0.75	0.453
% correct, median (IQR)	84.9 (55.5-91.0)	87.1(82.6-90.4)	Z^a=1.03	0.301
Mean (sd) reaction time for incorrect answers (ms)	270 (40)	388 (55)	t=-7.41	<0.001
Mean (sd) reaction time for correct answers (ms)	294 (42)	416(50)	t=-7.87	<0.001

^a Z-value from Mann-Whitney rank test