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.
... White, 1.36% African American, 0.15% Native American, 2.41% Asian, 0.03% Pacific Islander, 1.25% from other races, and 1.27% from two or more races. 5.85% of the population ...