Re: What is counter balancing and group matching?

Question: What is counter balancing and group matching?

I am an AP Psychology teacher teaching experimentation. In looking at the control condition of an experiment, what are the above terms and how are they control techniques? I have 14 psych books and cannot find this anywhere. My kids want to know! Thanks a bunch!!!

"Counter balancing" and "group matching" come from the area of study known as "Design of Experiments" or sometimes "Experimental Design". When an experiment is performed, the scientist gets back data. Design of experiments theory tells an experimenter how best to set up the experiment in order to get data that is useful as evidence for what the experimenter intends to prove. The Research Methods Knowledge Base, authored by William Trochim, has an has an excellent introduction to all facets of social research methods, including design of experiments.

Let's look at counter balancing first, since that's a bit simpler than group matching. Suppose that I'm running an experiment to test the effects of giving extra protein to students two hours before administering a reading test and a mathematics test. Here the sequence of testing might affect the outcome. If a student has a mathematics phobia, then giving the math test first could leave the student in no condition to do well on the reading test. Similarly, giving a reading test to a student might help or hinder their performance on a math test. To make this effect as small as possible, a counter balanced experiment would give half the students the math test first and the reading test second, and half the students the reading test first and the math test second. If there was a third test in history, there needs to be six groups where the order of test taking is either math, read, history, or math, history, read, or read, math, history, or read, history, math, or history, math, read, or history, read, math. You can see that as the number of tests grows, the number of groups required increases very fast. This webpage describes an experiment where counter balancing was used.

Group matching attempts to use data that has been collected previously. In an idea situation, an experimenter could randomly assign people to groups. For example one randomly chosen group gets the drug, while another randomly chosen group does not. Real life is rarely so nice, and often people are chosen to get a drug based on factors that are far from random. Matching attempts to use data about subjects so that the two groups are still at least somewhat comparable. For instance, suppose we gave a drug to everyone at a particular college, so most of the participants where between 18-22 years of age. We now want to find a second group to be our control group. It wouldn't make sense to draw our control group from a set of kindergartners or from a PTA meeting. Instead we should try to find a group of people as similar to the group that took the drug as possible. Perhaps other students from a similar school could be used. Group matching is a quasi-experimental design because the groups weren't really chosen randomly, so it doesn't qualify as a true experimental design.

Mark Huber