The non-equivalent group design is very similar to the basic true experiment design, the only differences being the selection of study participants (non-random selection) and the location of the study (field setting not laboratory) The time series design follows the basic design of the non-equivalent group; the difference here is that observations are made at a number of time intervals pre-test and a number of time intervals post-test. Longitudinal observations provide substantially more observational data and more detail on progressive change or continuity.