Table 1.

Sample size, mean age, and standard deviation by country, age group, gender, and survey year

	1985/1986			2014
	n	Mean age	SD	n	Mean age	SD
Finland
11‐year‐old boys	578	11.7	0.29	963	11.8	0.28
11‐year‐old girls	589	11.6	0.29	1020	11.8	0.27
13‐year‐old boys	465	13.6	0.30	943	13.8	0.30
13‐year‐old girls	461	13.6	0.30	944	13.8	0.30
15‐year‐old boys	543	15.7	0.31	956	15.8	0.31
15‐year‐old girls	546	15.6	0.29	1009	15.8	0.29
Norway
11‐year‐old boys	720	11.5	0.30	689	11.6	0.32
11‐year‐old girls	642	11.4	0.29	700	11.6	0.31
13‐year‐old boys	612	13.4	0.30	505	13.6	0.31
13‐year‐old girls	690	13.4	0.30	540	13.6	0.32
15‐year‐old boys	667	15.5	0.30	454	15.6	0.29
15‐year‐old girls	624	15.4	0.30	495	15.5	0.30