Quasi experiments are studies which utilize planned and intentional treatments as the independent variable, but lack the feature of random assignment. Random assignment is a key feature of true experiments so technically, quasi experiments are not considered to be true studies. Although, they can possess a pre and post design method, control groups and treatment groups, which are characteristics of true experiments1.
Quasi experiments are rather similar to natural experiments, with the main difference being that the independent variable, the treatment, is consciously chosen. There is nothing unintentional about the variable used. The independent variable can be either continuous or categorical in nature. Although, due to the bias nature of selection with these experiments, a researcher can never be completely sure whether the independent variable is causing a change in the dependent variable or if it is simply the result of an exogenous factor1.
Quasi experiments tend to generate more casual relationships. Often comparison groups are used to make inferences. However, these groups are not truly control groups because the selection of subjects to each group does not follow a randomized process.
For example, a study done in Scotland analyzed whether there was a link between implementing a walking program for children to travel to school and influencing children to continue to walk to school throughout the year2. A comparison was then made with another school close by which lacked this program, but was similar in terms of demographics and socioeconomic culture2. This illustrates the non-randomized nature of quasi-experiments because the subjects used did not have a choice over which school they attended. This study was then used to make inferences on whether this type of program would be helpful in encouraging a culture of walking to school.
1. National Center for Technology Innovation. (2014). Quasi-Experimental Study. Retrieved from: http://www.nationaltechcenter.org/index.php/products/at-research-matters/quasi-experimental-study/
2. Sagepub. (2014). Natural and Quasi Experiments. Retrieved from: http://www.sagepub.com/upm-data/33935_Chapter13.pdf