## Abstract

Information on disease and associated events, such as productivity, can be obtained from surveys. These involve counting members of an aggregate of units and measuring their characteristics. If all animals in a population are investigated then the survey is a census. The validity of sampling theory is based on the assumption that an aggregate of units can be divided into representative subâunits, and that characteristics of the aggregate can be estimated from the subâunits. There are two main types of sampling: nonâprobability sampling and probability sampling. The choosing of sample size depends on nonâstatistical and statistical considerations. Optimizing the number of herds and the number of animals selected in twoâstage sampling to demonstrate freedom from disease is an important consideration. The sampleâsize calculation, accommodating imperfect tests, is a twoâstage procedure, involving determination of the number of aggregates to be sampled, and the number of animals to be sampled in each aggregate.

Original language | English |
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Title of host publication | Veterinary Epidemiology: Fourth Edition |

Publisher | Wiley-Blackwell |

Pages | 270-295 |

Number of pages | 26 |

Edition | 4th |

ISBN (Electronic) | 9781118280249 |

ISBN (Print) | 9781118280287 |

DOIs | |

Publication status | Published - 27 Nov 2017 |

## Keywords

- Census
- Imperfect tests
- Non-probability sampling
- Probability sampling
- Sample optimization
- Sample surveys
- Sampling theory
- Surveys