Table 1.

Sample sizes, gender distribution (%), mean age and standard deviation (SD) in years of the participants from six age groups.

	10 years	11 years	12 years	13 years	14 years	15 years
Number of participants	157	128	193	278	279	215
Female (%)	78 (50)	69 (54)	86 (45)	144 (52)	143 (51)	106 (49)
Mean age	10.30	11.26	12.59	13.44	14.39	15.47
SD age	0.32	0.30	0.26	0.29	0.28	0.27

The Chi square analyses indicated that gender distribution did not differ across the age groups (X² = 34.65, p = 0.60).