Table 2.

Objectively measured physical activity at baseline and follow-up periods across grade cohorts and total study sample.

	Grade 9 (n = 296)		Grade 10 (n = 151)		Total (n = 447)		P value
	n	%	n	%	n	%
Students with valid PA at each time point
T0: Prepolicy	296	(100.0)	151	(100.0)	477	(100.0)	N.A.
T1: February 2009–June 2009	99	(33.4)	68	(45.0)	167	(37.4)	N.A.
T2: September 2009–January 2010	73	(24.7)	21	(13.9)	94	(21.0)	N.A.
T3: February 2010–June 2010	138	(46.6)	94	(62.3)	232	(51.9)	N.A.
T4: September 2010–January 2011	54	(18.2)	0	(0.0)	54	(12.1)	N.A.
T5: February 2011–June 2011	122	(41.2)	2	(0.0)	124	(27.7)	N.A.
T6: September 2011–December 2011	44	(14.9)	0	(0.0)	44	(0.09)	N.A.
Time points contributed per student, mean ± SD	2.79	±1.18	2.23	±0.850	2.60	±1.11	<0.0001a
Baseline PA
Students with baseline data	296	(100.0)	151	(100.0)	447	(100.0)	N.A.
Minutes per day, mean ± SD	58.7	±24.1	57.6	±23.8	58.3	±24.0	0.5890a
Accumulated ≥ 30 min/day	265	(89.5)	131	(86.8)	396	(88.6)	0.3833b
Accumulated ≥ 60 min/day	138	(46.6)	61	(40.4)	199	(44.5)	0.2104b
PA at students' last followup
Students with ≥ 1 followup	230	(77.7)	110	(72.9)	340	(76.1)	0.3304b
Minutes per day, mean ± SD	42.6	±23.5	47.2	±23.9	44.1	±23.7	0.0485a
Accumulated ≥ 30 min/day (% with ≥ 1 followup)	149	(64.8)	82	(74.6)	231	(67.9)	0.0712b
Accumulated ≥ 60 min/day (% with ≥ 1 followup)	46	(20.0)	25	(22.7)	71	(20.9)	0.5627b
PA change from baseline to last followup
Students with ≥ 1 followup	230	(77.7)	110	(72.9)	340	(76.1)	0.3304b
Change (min/day), mean ± SD	−14.6	±24.7	−11.1	±29.0	−13.4	±26.2	0.2701a
Percentage change (%), mean ± SD	−18.7	±48.8	−10.0	±51.0	−15.9	±49.6	0.1871a

^aWilcoxon two-sample test used to compare across grade cohorts.

^bChi-square test used to compare across grade cohorts.

N.A.: denotes not applicable.