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Table 5 Sample size estimates for GP Presentation Study estimating a single UK-wide pyramid.

From: Methods for determining disease burden and calibrating national surveillance data in the United Kingdom: the second study of infectious intestinal disease in the community (IID2 study)

  England Wales
Organism Baseline incidence* Reduction to be detected Person-years GP practices Person-years GP practices
Campylobacter 4.10% 20% 115,000 20 7,000 2
Salmonella 0.16% 50% 41,000 7 3,000 1
Salmonella 0.16% 40% 67,000 12 4,000 1
Salmonella 0.16% 30% 127,000 22 8,000 2
Salmonella 0.16% 20% 302,000 51 18,000 3
C. perfringens 0.13% 20% 364,000 61 22,000 4
  Scotland Northern Ireland UK
Organism Person-years GP practices Person-years GP practices Person-years GP practices
Campylobacter 12,000 2 4,000 1 138,000 25
Salmonella 5,000 1 2,000 1 51,000 10
Salmonella 7,000 2 3,500 1 81,500 16
Salmonella 13,000 3 4,500 1 152,500 28
Salmonella 31,000 6 10,500 2 361,500 62
C. perfringens 38,000 7 13,000 3 434,500 75
  1. * Incidence of GP presentation in original IID study
  2. Note: Based on the ability to detect at least a 20% reduction in incidence with 90% power and 95% precision. Required number of person-years and GP practices (assuming an average GP practice size of 6,000 patients) by country, based on the relative populations of the 4 countries.