Quasi-experimental research designs evaluate interventions by assigning participants to different intervention conditions in a nonrandom process. This entry briefly discusses the rationale behind quasi-experimental research designs and describes several of the most prominently used designs in abnormal and clinical psychology research.


Randomized controlled trials (RCTs), in which participants are randomly allocated to different intervention conditions, are generally considered the most trustworthy research method to assess intervention effectiveness. However, RCTs may not be practical or ethical for evaluating an intervention, for instance, if a clinic refuses to choose via a random process which treatment participants receive. These challenges leave some researchers, who nevertheless agree in principle with using RCTs, to consider using rigorous nonrandomized study designs instead, so that research evidence exists for more interventions than ...

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