A true experiment has one main component - randomly assigned treatments. This translates to every participant having an equal chance of being assigned to any treatment.

A quasi-experiment has the set up of an experiment, but is simply defined as not a true experiment. Since the main component of a true experiment is randomly assigned treatments, this means a quasi-experiment does not have randomly assigned treatments. Assignment to a given treatment condition is based on something other than random assignment.

examples: gender, age, a cutoff score on a test, a particular medical condition.

Caution: In quasi-experiments we have not potentially controlled for confounding effects, so causal inference may not be valid.