Читать книгу The Pocket Guide to Critical Appraisal - Iain K. Crombie - Страница 12

Surveys take samples from a target group or population. The idea behind this is that a well‐taken sample contains almost as much information as would come from studying the whole population. In principle, surveys obtain a complete list of the group or population of interest from which a sample of individuals is selected for further study. The selection is carried out randomly (not haphazardly), such that each individual has an equal chance of being chosen. In practice, a complete list may not be available and alternative approaches such as cluster sampling can be used (these more complicated designs are not described here). The important points are that selection of individuals uses random sampling and that the sample obtained is representative of a target population.