Sampling strategies

Through the study of disease in populations, a large amount of information can be gained - which will be increased if more members of the population are sampled. However, this is rarely feasible from either a logistical or an economic perspective, meaning that methods of selecting animals from the population are required. Despite this, censuses are carried out intermittently in many countries for both livestock and for humans. These are a form of descriptive study which aims to collect information about every member of the population of interest (the source population), although information regarding disease is rarely routinely collected in these studies. Surveys are another type of descriptive study which are commonly performed, and aim to select a sample from the population. Similarly, in most analytic studies, a sample of the population must be selected. This sampling process poses potential problems, as it must both select a sufficient number of individuals in order to be useful (whilst not sampling more than is required) for the purposes of the study, and must ensure that the biases in the selection process are minimised.