Background

Definition: Quasi-experiments are studies that aim to evaluate interventions but that do not use randomization. Similar to randomized trials, quasi-experiments aim to demonstrate causality between an intervention and an outcome. These studies can use both preintervention and postintervention measurements as well as nonrandomly selected control groups (Harris et al., 2006). 

Because quasi-experiments were developed by researchers with psychological orientations, they have been published more often by such researchers (Grant & Wall, 2009). However, currently they are widely used in organizational research, in the context of business and educational settings, in medical informatics, in a hospital or public health setting, in a word – in situations when researchers often choose not to randomize the intervention for one or more reasons: 

1. Ethical considerations;
2. Difficulty of randomizing subjects; 
3. Difficulty to randomize by locations (e.g., by wards);
4. Small available sample size;
5. A need to intervene quickly (Harris et al., 2004).