Definition 4.2 An elementary unit, population unit or simply element is the entity carrying the information that is intended to be collected. \(\\\)
The elementary unit can be an object, animal or person. In certain cases there is more than one way to define the elementary unit, where understanding by the experts involved is necessary. The elementary unit is one of the most important definitions in the scientific field, as it is the basis for all construction of research hypotheses.
Example 4.1 (Electoral research I) In an electoral survey, the voter is classified as an elementary unit.
Definition 4.3 The sampling unit is a composition of one or more elementary units. \(\\\)
Example 4.2 (Electoral research II) In a street electoral survey, the voter is also the sampling unit. If interviews are carried out from house to house, the household becomes a sampling unit, i.e., a set of elementary units (voters).
In relation to the information from a study, an assessment must initially be made of the databases already available and then proceed with the assessment of the feasibility of a more specific data collection. This survey involves putting together a sampling plan, hiring, training and maintaining people for collection, creating response protocols as well as generating and analyzing databases. If it is decided to carry out such a survey, lists listing population and sample units will be necessary. In the absence of such lists, reference systems are used, which are sources that describe the universe to be investigated. This may be reasonably up-to-date information, such as maps, censuses, or collated lists.