Table 1.

Demographic characteristics and drug use profile among former crystalline-heroin users (n = 20 in each group)

Variable	Groups		t-test
	Experimental group (mean ± SD)	Control group (mean ± SD)	df	P
Age (year)	37.950 ± 8.035	38.400 ± 7.014	38	0.851
Education (year)	11.700 ± 2.848	11.450 ± 2.416	38	0.766
Age of onset (year)	32.850 ± 66.175	30.950 ± 7.897	38	0.402

SD: Standard deviation; df: Degree of freedom