In different statistical disciplines, the statistical unit is the source of a random variable. There are different ways to study a unit and different names applied

1. We may be interested in a unit because we intend to generalize from observations on a few units to a statistical assembly of units. Opinion polling and survey sampling provide well known examples of this type of research.
2. We may be interested in the dynamics of a unit, how its observable characteristics change from time to time. Economic studies of business firms provide an example of this type of research. (See dynamic model.)
3. We may be interested in the internal functioning of a unit which we can characterize as a statistical assembly. This kind of research often involves interference with the unit such as subjecting it to a treatment or even dissection, in some cases. Field experimentation and clinical trials. are examples.

See also: statistical model