Table 2.

Relative frequencies of Stomach ache among grade 5, 7 and 9 students, distributed by gender and menarche

	Boys	Girls no period	Girls period
	n = 9153	n = 3676	n = 5446
Every day	2.1%	3.7%	5.5%
More than once a week	5.5%	8.0%	13.6%
Once a week	11.3%	15.5%	16.8%
About once a month	29.0%	28.7%	44.0%
Seldom or never	52.2%	44.1%	20.0%