Research types on this page are modeled after those listed in the Introduction to Measurement and Statistics website created by Dr. Linda M. Woolf, Professor of Psychology at Webster University. The definitions are based on Dr. Woolf's explanations. Go to Dr. Woolf's website for much more information as well as practice pages.
Researchers observe participants but do not attempt to influence them.
Researchers control conditions to examine how one variable affects the other(s). Participants are assigned to random groups (at least two). There is a control group that does not experience or receive the variable being examined and a experimental group that does experience or receive the variable being examined. The groups are compared to examine the effect of the variable being investigated.
In experiments, causation can be explored.
A quasi-experiment is like an experiment, but the groups cannot be assigned. Quasi-experiments use pre-existing groups.