Conglomerates can be geographical areas, institutions or organizations (cf. Berganza, 2005: 188-189). It is not individuals who are extracted as basic units but the groups or conglomerates of individuals, such as families, neighborhoods, urban centers, etc. They can be:

• Area or surface sample: It is a geographical sample and refers to all those physical units located in a given territory.
• Successive samples: In turn, they are divided into: 1) "before after" and 2) trends. "Before-after" samples are those in which the measure is used to test the effects of an action, fact, or changes introduced between the two successive measures. Trend samples are those that are obtained by conducting more than two surveys without being determined by a specific fact.
• Samples by stages: They are similar to the successive samples, they are made from a large sample on which a smaller sample is extracted, in order to perform an in-depth study. If it is done in two stages it is two-stage and if it is done in several stages it is multi-stage. Units are selected in different stages to form a sample of individuals.