Editing Statistical unit (section)

==Experimental and sampling units==
Units are often referred to as being either '''experimental units''' or '''sampling units''':

* An "experimental unit" is typically thought of as one member of a set of objects that are initially equal, with each object then subjected to one of several experimental treatments. Put simply, it is the smallest entity to which a treatment is applied.
* A "sampling unit"  (or [[unit of observation]]) is typically thought of as an object that has been sampled from a [[statistical population]]. This term is commonly used in [[opinion polling]] and [[survey sampling]].

For example, in an experiment on educational methods, methods may be applied to classrooms of students. This would make the classroom as the experimental unit. Measurements of progress may be obtained from individual students, as observational units. But the treatment (teaching method) being applied to the class would not be applied independently to the individual students. Hence, the student could not be regarded as the experimental unit. The class, or the teacher (who applies the method, if he/she has multiple classes), would be the appropriate experimental unit.