A statistical model is used in applied statistics. Three basic notions are sufficient to describe all statistical models.
We choose a statistical unit which we will observe directly. Multiple observations of the same unit over time is called longitudinal research[?]. Observations of a variety of statistical attributes[?] is a common way of studying relationships among the attributes of a single unit.
We may really be interested in a statistical population (or set) of similar units rather than in any statistical unit per se. Survey sampling offers an example of this type of application.
... are 196 people, 69 households, and 58 families residing in the township. The population density is 2.1/km² (5.4/mi²). There are 76 housing units at an average ...