Table 4.
Sample size calculations for prospective cohort study estimating a single UK-wide pyramid.
| England | Wales | |||||
|---|---|---|---|---|---|---|
| Organism/condition | Baseline incidence1 | Reduction to be detected | Person-years | GP practices | Person-years | GP practices |
| All IID | 19.20% | 20% | 2,000 | 20 | 200 | 2 |
| Severe cases* | 6.00% | 20% | 7,000 | 70 | 400 | 4 |
| Campylobacter | 0.87% | 20% | 500,000 | 5,000 | 2,400 | 24 |
| Salmonella | 0.22% | 20% | 500,000 | 5,000 | 9,500 | 95 |
| Campylobacter+Salmonella | 1.10% | 20% | 200,000 | 2,000 | 2,000 | 20 |
| Campylobacter+Salmonella+ C. perfringens | 1.34% | 20% | 100,000 | 1,000 | 1,600 | 16 |
| Scotland | Northern Ireland | UK | ||||
| Organism/condition | Person-years | GP practices | Person-years | GP practices | Person-years | GP practices |
| All IID | 200 | 2 | 65 | 1 | 2,465 | 25 |
| Severe cases* | 700 | 7 | 300 | 3 | 8,400 | 84 |
| Campylobacter | 4,200 | 42 | 1,400 | 14 | 508,000 | 508 |
| Salmonella | 16,400 | 164 | 5,500 | 55 | 531,400 | 532 |
| Campylobacter+Salmonella | 3,400 | 34 | 1,200 | 12 | 206,600 | 207 |
| Campylobacter+Salmonella+ C. perfringens | 2,800 | 28 | 1,000 | 10 | 106,200 | 107 |
* Severe cases are defined as those presenting to primary care
Note: Based on ability to detect a 20% decrease in incidence with 80% power and 95% precision. Required number of person-years and GP practices (recruiting 100 patients from each practice) by country, based on the relative populations of the 4 UK countries