To understand the function of an experimental group, one must first know what an experiment is, since that is the context in which experimental groups are found. An experiment is one of the techniques available to researchers in their study of human development. This research method attempts to determine the effect of one (or more) events or treatments on the behaviors of individuals. It accomplishes this by creating two or more equivalent groups of individuals and treating them exactly the same in all ways except for the event or treatment whose effect is being tested. If, after one group has received the treatment or experienced the event, there are now measurable differences between that group and the other(s), those differences are presumed to be due to the event or treatment.
The experimental group refers to the individuals who receive the treatment or experience the event that is of interest to the researcher. The group of research participants that does not receive the treatment is called the control group. The treatment or event that is manipulated is termed the independent variable, and the participants’ responses are the dependent variable.
To serve as an example, suppose a researcher is interested in the effects of watching television violence on children’s subsequent aggressive behavior. The independent variable is TV violence, and the dependent variable is some measure of the children’s aggression, perhaps the number of kicks or punches displayed against an inflatable doll during a 1-hour period. To create an experimental group, the researcher may have several children watch a 30-minute video that includes several episodes of violent acts. The researcher may have a control group of children watch a nonviolent video. The aggressive behaviors of both groups of children would then be observed and recorded, and the researcher would test whether the experimental and control groups differed in a significant way.
Many experiments employ more than one experimental group. For example, if a researcher is interested in what type of TV violence has the greatest influence on aggression, the researcher may have one group of children watch cartoon violence, a second group watch sports violence, and a third watch violence between human actors. A control group may still be included that would serve as a comparison for all three experimental groups.
Experimental and control groups are created to provide a comparison. Turning to our example again, we may find that subjects who watch a 30-minute violent video go on to display an average of 4.5 aggressive behaviors during that next hour. Only by including a control group of children who did not watch a violent video, and finding that they exhibited an average of 1.2 (or 8.9 or 4.6) violent behaviors during the next hour can we infer that the video increased (or decreased or had no effect on) children’s subsequent aggressive behavior.
It is critical that experimental and control groups be as equivalent as possible before the independent variable is manipulated. The preferred method for achieving equivalence is to randomly assign individuals into groups. In our example, that would mean making sure that each child had the same probability of being assigned to watch the violent video or nonviolent video. If children are allowed to decide for themselves which video they watch, it may turn out that children who choose to watch the violent video are more aggressive to begin with.
The experiment is considered the best research method available for inferring cause and effect. Observing naturally occurring behaviors is an effective descriptive technique. But it is the intentional assignment of subjects into equivalent experimental and control groups that makes causal inference possible.
References:
- Goodwin, J. (2003). Research in psychology: Methods and design (3rd ed.). Hoboken, NJ: Wiley.
- Green, D. (n.d.). Classics in the history of psychology.Retrieved from http://psychclassics.yorku.ca/Bandura/bobo.htm
- Oehlert, W. (2000). A first course in design and analysis of experiments. New York: Freeman.
- Schweigert, W. (1994). Research methods and statistics for psychology. Pacific Grove, CA: Brooks/Cole.
- Woolf, L. M. (n.d.). Developmental research Retrieved from http://www.webster.edu/~woolflm/methods/devresearchmethods.html