# Commission Decision of 20 December 2007 concerning a financial contribution from the Community towards a survey on the prevalence of Salmonella spp. and Methicillin-resistant Staphylococcus aureus in herds of breeding pigs to be carried out in the Member States (notified under document number C(2007) 6579) (2008/55/EC), Division 2.3.1: Primary sample size (first-stage sample size)

Extent: E+W+S+N.I.

A regular primary sample size calculation shall be conducted for the breeding holdings and a second regular primary sample size calculation shall be conducted for the production holdings. The primary sample size shall be the number of breeding holdings to be sampled and the number of production holdings to be sampled in each Member State and it shall be determined taking into account the following criteria, assuming simple random sampling:
(a) the total number of breeding holdings (breeding holdings, Part 1 of the Salmonella and MRSA surveys);
(b) the total number of production holdings (production holdings, Part 2 of the Salmonella and MRSA surveys);
(c) annual expected prevalence (p): 50 %;
(d) desired confidence level (Z): 95 %, corresponding to a Zα value of 1,96;
(e) accuracy (L): 7,5 %;
(f) using these values and the formula:
n ∞ = Z α 2 p 1–p L 2
The calculation shall be conducted firstly, for the breeding holdings and secondly, for the production holdings. In each case, the assumptions in steps c-e above are the same.
For practical purposes, if there are 100 000 or more holdings in either the breeding herds sampling frame or the production herds sampling frame then that population can be considered to be infinite and the number of holdings to be randomly selected from that sampling frame is 171 (see Table 1). Where the number of breeding herds or production herds is less than 100 000 a finite population correction factor is applied and fewer holdings need to be sampled as shown in Table 1.
As an example, if there are in a Member State 1 000 holdings belonging to the production holding group and 250 holdings belonging to the breeding holding group, 147 holdings must be sampled in the production holding group and 102 holdings must be sampled in the breeding holding group.
Table 1
Number of holdings with breeding pigs to sample in either part of the Salmonella and MRSA surveys as a function of the finite population size (total number of holdings with breeding pigs in the Member States)
Number of holdings with breeding pigs (N)
Sample size (n) for finite population size 7,5 % accuracy
100 000
171
10 000
169
5 000
166
2 000
158
1 000
147
500
128
250
102
150
80
125
73
100
64
90
59
80
55
70
50
60
45
50
39
40
33
30
26
20
18
10
10
Non-response shall be anticipated e.g. by increasing the sample size in each group by 10 %. Any unsuitable holding shall be replaced in the process of the Salmonella and MRSA surveys (see Section 2.2.1).
In case an estimation of the number of ‘breeding holdings’ is not possible prior to the start of the survey, a number of holdings shall be selected for sampling as in Table 1 based on the total number of holdings with sows (X holdings). The number of holdings to be sampled shall be increased by at least 30 % ((X + 30 %) holdings). Prior to the survey, the competent authority shall identify a number of breeding holdings, equal to at least this additional 30 %. While visiting the farms, the holding will be classified as breeding or production holding according to the definitions above.

---
Source: https://www.legislation.gov.uk/eudn/2008/55/annex/I/part/A/division/2/division/2.3/division/2.3.1 (the official version)
Page: https://openlegislation.uk/eu-decision-2008-55/annex-I/part-A/division-2/division-2.3/division-2.3.1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.