Categories of Quasi-Experimental Study Designs:

A. Quasi-experimental designs without control groups

B. Quasi-experimental designs that use control groups but no pretest

C. Quasi-experimental designs that use control groups and pretests

D. Quasi-experimental designs that use control groups, pretests and postest

E.  Interrupted time-series designs

In research literature, there is a relative hierarchy within these categories of study designs, with the last two designs being considered the higher rated categories in terms of establishing causality (Harris et al., 2006). The main use of the design with pretests and postests, or controlled before and after studies, as Muir Gray (2009) defines them, is “to asses the impact of changes in health service organization or policy” (p. 164). An interrupted time-series design is used to investigate complex interventions immediately and over time when rendomization is not possible or practical, such as a change in policy: “guideline implementation strategies in primary care or a mass media campaign” (Muir Gray, 2009, p. 167).