Randomised feasibility trial of a teaching assistant led extracurricular physical activity intervention for 9 to 11 year olds: Action 3:30

Table 8 Sample size calculations based on detecting a 10 minute difference in weekday MVPA using a cluster size of 24 and 12 per school

Outcome^a	Cluster size	ICC^b	α	Power (β)	n required per arm^c	n schools/arm	N per arm inflated for attrition^d	Total N^e
Cluster size = 24
MVPA/weekday (min)	24	0.12977	5%	80%	360	15	450	900
MVPA/weekday (min)	24	0.12977	5%	90%	456	19	570	1140
MVPA/weekday (min)	24	0.12977	1%	90%	624	26	780	1560
		ICC^f
MVPA/weekday (min)	24	0.06534	5%	80%	240	10	300	600
MVPA/weekday (min)	24	0.06534	5%	90%	312	13	390	780
MVPA/weekday (min)	24	0.06534	1%	90%	408	17	510	1020
Cluster size = 12
	Cluster size	ICC ^b	α	Power (β)	n required per arm ^c	n schools/arm	N per arm inflated for attrition ^d	Total N ^g
MVPA/weekday (min)	12	0.12977	5%	80%	204	17	255	510
MVPA/weekday (min)	12	0.12977	5%	90%	276	23	345	690
MVPA/weekday (min)	12	0.12977	1%	90%	384	32	480	960
		ICC^f
MVPA/weekday (min)	12	0.06534	5%	80%	156	13	195	390
MVPA/weekday (min)	12	0.06534	5%	90%	204	17	255	510
MVPA/weekday (min)	12	0.06534	1%	90%	276	23	345	690

^aTarget difference = 10 minutes of MVPA per weekday.
^bobserved ICC (95% CI) was 0.06534 (0.00091 to 0.12977); upper limit of 95% CI used.
^ccluster size of 24.
^destimated attrition = 20% (~6 per cluster).
^ebased on 30 pupils per school (i.e. 24 + 6).
^fPoint estimate of ICC used.
^gbased on 15 pupils per school (i.e. 12 + 3).

ISSN: 1479-5868