Table 3 Power calculations for intermediate and long-term outcomes
| Â | Â | Â | 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) |
| Â | Â | Â | Â | Â | Â | Deprivation (2 levels) | Â | Deprivation (2 levels) |
| Â | Â | Â | Â | Â | Â | Age (2 levels) | Â | Â |
All (community population) |  |  |  | N = 1280 | N = 640 | N = 4074 | N = 2037 | |
| Â | Access to tobacco: If try buy, likely to be successful1 | 32%-25% | 680 | 999 | >0.80 | 0.80 | >0.99 | >0.99 |
| Â | Access to tobacco: If try buy, likely to be successful2 | 32%-22% | 328 | 479 | >0.99 | >0.80 | >0.99 | >0.99 |
| Â | Awareness tobacco marketing in shops1 | 81%-22% | 14 | 19 | >0.99 | >0.99 | >0.99 | >0.99 |
| Â | Awareness tobacco marketing in shops2 | 81%-71% | 305 | 445 | >0.99 | >0.99 | >0.99 | >0.99 |
| Â | Perceived prevalence regular smoking1 | 62%-46% | 164 | 238 | >0.99 | >0.99 | >0.99 | > 0.99 |
| Â | Perceived prevalence regular smoking2 | 62%-52% | 404 | 591 | >0.99 | >0.80 | >0.99 | >0.99 |
| Â | Incidence regular smoking3 | 4%-2% | 1239 | 1797 | >0.80 | Â | >0.99 | >0.80 |
| Â | Incidence any smoking3 | 9%-7% | 2987 | 4396 | Â | Â | >0.80* | Â |
| Â | Prevalence regular smoking3 | 13%-10% | 1841 | 2707 | Â | Â | >0.99 | >0.80 |
| Â | Prevalence regular smoking3 | 13%-9% | 1009 | 1478 | >0.80 | Â | >0.99 | >0.80 |
Current smokers |  |  |  | N = 136 | N = 68 | N = 482 | N = 241 | |
| Â | Purchase tobacco from shops4 | 55%-43% | 412 | 603 | Â | Â | >0.80 | 0.82* |
| Â | Purchase from Supermarkets4 | 12%-5% | 389 | 563 | Â | Â | >0.80 | 0.85* |
| Â | Purchase from Small Shops4 (increase after POS Supermarkets | 44%-56% | 411 | 603 | Â | Â | >0.80 | 0.82* |
| Â | Purchase from Small Shops4 | 44%-32% | 393 | 575 | Â | Â | >0.80 | 0.84* |
| Â | Access to tobacco: If try buy, likely to be successful | 32%-20% | 408 | 596 | Â | Â | >0.80 | 0.83 |
| Â | Awareness tobacco marketing in shops1 | 81%-22% | 14 | 19 | >0.99 | >0.99 | >0.99 | 0.99 |
| Â | Awareness tobacco marketing in shops2 | 81%-71% | 305 | 445 | Â | Â | >0.80 | 0.80* |
| Â | Perceived prevalence regular smoking2 | 62%-50% | 404 | 591 | Â | Â | 0 | 0.83* |
Ever smokers |  |  |  | N = 422 | N = 212 | N = 1287 | N = 644 | |
| Â | Purchase tobacco from shops4 | 23%-16% | 530 | 776 | >0.80* | Â | >0.99 | 0.87 |
| Â | Purchase from Supermarkets4 | 4%-1% | 489 | 697 | >0.80* | Â | >0.99 | 0.85* |
| Â | Purchase from Small Shops4 (increase after POS Supermarkets ) | 18%-25% | 568 | 832 | >0.80* | Â | >0.99 | 0.85 |
| Â | Purchase from Small Shops4 | 18%-12% | 588 | 859 | >0.80* | Â | >0.80 | >0.80* |
| Â | Access to tobacco: If try buy, likely to be successful2 | 32%-22% | 408 | 596 | >0.80 | Â | >0.99 | >0.80 |
| Â | Awareness tobacco marketing in shops1 | 81%-22% | 14 | 19 | >0.99 | >0.99 | >0.99 | >0.99 |
| Â | Awareness tobacco marketing in shops2 | 81%-71% | 305 | 445 | >0.80 | Â | >0.99 | >0.99 |
| Â | Perceived prevalence regular smoking2 | 62%-52% | 404 | 591 | >0.80 | Â | >0.99 | >0.80 |