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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.