Table 1.

Study population by sex, age group, social class, year and physical inactivity.

	Data collection wave
	1991	1994	1998	2002	2006	2010	2014	Total
Response rate	90.2%	90.9%	88.0%	89.3%	88.8%	86.3%	85.8%	88.2%
N	1860	4046	5205	4824	6269	4922	4534	31,660
N included in this studya	1837	3994	5165	4771	6210	4865	4132	30,974
Pct. boys	50.2	49.9	49.6	48.7	49.3	50.1	48.6	49.4
Pct. girls	49.8	50.1	50.4	51.3	50.7	50.0	51.4	50.6
Pct. 11-year-olds	31.7	31.6	33.9	36.4	37.6	37.2	30.5	34.7
Pct. 13-year-olds	34.7	34.7	35.7	33.7	35.6	33.7	35.5	34.8
Pct. 15-year-olds	33.6	33.7	30.4	29.9	26.9	29.1	34.1	30.5
Pct. high social class	25.8	30.3	25.8	22.1	22.3	32.8	38.2	27.8
Pct. middle social class	47.3	44.2	45.9	48.7	40.0	35.9	37.0	42.2
Pct. low social class	18.2	16.7	20.9	18.7	18.4	16.2	14.4	17.8
Pct. unclassifiable	8.8	8.8	7.5	10.5	19.4	15.1	10.5	12.2
Pct. physically inactive	8.1	9.4	10.2	10.3	5.1	7.5	6.6	8.0

^aNon-respondents of the physical activity question excluded.