Table 1. Summary characteristics of the sample by survey year.

	Survey year
	1985	1997	2004	2010	2015
Child response rates (%)	68	87	66	57	63
Sample size	1270	5518	5407	8058	7555
Available BMI data (n)	896	5402	5395	7734	7374
Available waist-to-height data (n)	1269	4391	5399	7850	7354
Boys (%)	49	53	51	52	48
Age years (mean, range)
Primary school	10.8 (8.1–15.7)	9.4 (5.1–13.0)	8.6 (4.2–13.1)	8.4 (4.2–15.7)	8.5 (3.3–13.3)
High school	14.5 (12.3–16.2)	14.2 (11.4–17.3)	14.5 (12.2–17.3)	14.3 (10.2–19.9)	14.3 (12.4–17.2)
Socioeconomic status (%)
Low	32.1	27.4	23.9	29.0	24.5
Middle	39.4	39.6	35.9	37.9	34.4
High	28.6	33.0	40.2	33.1	41.1