Table 1. Sample characterization of Portuguese Adolescents .

	Male		Female		Total
	N	%	N	%	N	%
	171	38.3	276	61.7	447	100.0
Age (yr)
12	31	18.2	27	9.8	58	13.0
13	29	17.0	38	13.8	67	15.0
14	18	10.5	34	12.3	52	11.6
15	28	16.4	27	9.8	55	12.3
16	16	9.4	34	12.3	50	112
17	16	9.4	29	10.5	45	10.1
18	18	10.5	43	8.3	61	13.6
19	15	1.8	44	16.0	59	13.0
Grade
7	34	19.9	26	9.4	59	13.4
8	26	15.2	38	13.8	64	14.3
9	19	11.1	33	12.0	52	11.6
10	30	17.5	38	13.8	68	15.2
11	19	11.1	32	11.6	51	11.4
12	43	25.2	109	39.5	152	34.0
Parents´educational level
≤ 4 grade	3	2.0	16	6.9	19	4.3
5-12 grade	105	61.4	134	48.6	239	53.5
> 12 grade	30	17.5	37	13.4	67	15.0
Without information	33	19.1	89	31.1	122	27.2
Crowding índex
≤1.0	135	78.9	247	89.5	382	85.5
>1.0	8	4.7	12	4.3	20	4.5
Without information	28	16.4	17	6.2	45	10.0
Residential area
Rural	100	58.5	192	69.6	292	65.3
Urban	71	41.5	84	30.4	155	34.7