Table 3.

Power calculations for intermediate and long-term outcomes

			Sample size required at 0.80 power with two-tailed test		Sample before and 1 year after POS Supermarket (4 S2 & 4 S4 from 4 schools 24 pupils each class 85% response rate)		Sample before Small Shops POS and 2 years after (all pupils attending schools, 4 schools, school size 1200 pupils, response rate 85%)
	Outcome	Change	p < .05	p < .01	4 schools combined	Urbanisation (2 levels)	4 schools combined	Urbanisation (2 levels)
						Deprivation (2 levels)		Deprivation (2 levels)
						Age (2 levels)
All (community population)					N = 1280	N = 640	N = 4074	N = 2037
	Access to tobacco: If try buy, likely to be successful1	32%-25%	680	999	>0.80	0.80	>0.99	>0.99
	Access to tobacco: If try buy, likely to be successful2	32%-22%	328	479	>0.99	>0.80	>0.99	>0.99
	Awareness tobacco marketing in shops1	81%-22%	14	19	>0.99	>0.99	>0.99	>0.99
	Awareness tobacco marketing in shops2	81%-71%	305	445	>0.99	>0.99	>0.99	>0.99
	Perceived prevalence regular smoking1	62%-46%	164	238	>0.99	>0.99	>0.99	> 0.99
	Perceived prevalence regular smoking2	62%-52%	404	591	>0.99	>0.80	>0.99	>0.99
	Incidence regular smoking3	4%-2%	1239	1797	>0.80		>0.99	>0.80
	Incidence any smoking3	9%-7%	2987	4396			>0.80*
	Prevalence regular smoking3	13%-10%	1841	2707			>0.99	>0.80
	Prevalence regular smoking3	13%-9%	1009	1478	>0.80		>0.99	>0.80
Current smokers					N = 136	N = 68	N = 482	N = 241
	Purchase tobacco from shops4	55%-43%	412	603			>0.80	0.82*
	Purchase from Supermarkets4	12%-5%	389	563			>0.80	0.85*
	Purchase from Small Shops4 (increase after POS Supermarkets	44%-56%	411	603			>0.80	0.82*
	Purchase from Small Shops4	44%-32%	393	575			>0.80	0.84*
	Access to tobacco: If try buy, likely to be successful	32%-20%	408	596			>0.80	0.83
	Awareness tobacco marketing in shops1	81%-22%	14	19	>0.99	>0.99	>0.99	0.99
	Awareness tobacco marketing in shops2	81%-71%	305	445			>0.80	0.80*
	Perceived prevalence regular smoking2	62%-50%	404	591			0	0.83*
Ever smokers					N = 422	N = 212	N = 1287	N = 644
	Purchase tobacco from shops4	23%-16%	530	776	>0.80*		>0.99	0.87
	Purchase from Supermarkets4	4%-1%	489	697	>0.80*		>0.99	0.85*
	Purchase from Small Shops4 (increase after POS Supermarkets )	18%-25%	568	832	>0.80*		>0.99	0.85
	Purchase from Small Shops4	18%-12%	588	859	>0.80*		>0.80	>0.80*
	Access to tobacco: If try buy, likely to be successful2	32%-22%	408	596	>0.80		>0.99	>0.80
	Awareness tobacco marketing in shops1	81%-22%	14	19	>0.99	>0.99	>0.99	>0.99
	Awareness tobacco marketing in shops2	81%-71%	305	445	>0.80		>0.99	>0.99
	Perceived prevalence regular smoking2	62%-52%	404	591	>0.80		>0.99	>0.80

1 Change based on findings McNeil et al. [14] paper on the removal of Point of Sale tobacco displays in Ireland.

2 Starting percentage based on findings McNeil et al. [14] paper on the removal of Point of Sale tobacco displays in Ireland.

3 Starting percentages based on findings latest published results from HBSC [19] and SALSUS [18] studies.

4 Starting percentages based on findings latest published results from SALSUS [18].

* Denotes power calculation for a one-tailed test. Blank cells are underpowered to detect a significant change.