In psychology, having independent groups simply refers to testing a hypothesis with two or more groups that do not overlap each other. For example, one group is often the control group, and the other is the experimental group. These are two independent groups that are not meant to influence each other in any way.
During a hypothesis testing, both groups start off the same. The control group is left unchanged, while some kind of change is added to the experimental group. The results of the change are measured by comparing the experimental group to the control group. This is why it is important that each group stay independent, or it influences the outcome of the experiment, according to SimplyPsychology.org. The number of groups involved changes depending on how many experimental groups there are. There is usually only one control group, but there are often more experimental groups compared to the control group.
The key for holding a successful independent group research experiment is for the controller to take note of the differences between each participant. It is usually best to keep each participant as similar as possible. If a group is made up of people of different social backgrounds, sexes and ages, their reactions to the experiment are all different. These differences are called participant variables.