Another variable that can affect experiment results is order effects. Order effects occur when the way that participants perform tasks affects the results. We have already looked at order effects, but let’s return to this briefly.
Say we carry out an experiment to see if eating a vitamin tablet before a test helps with exam performance and we use a repeated measures design. The first time the participants sit the exam, we give them a sweet and tell them it’s a vitamin tablet. The second time they do the exam, we give them a vitamin tablet. If participants do better on the second exam it could be because of the affect of the vitamin tablet, or, it could be because they’ve got better at answering the questions – the difference in performance would be down to order effects but it would appear to be the affect of the vitamin tablet.
|Variable||Way to Control For It|
|Order Effects||Counterbalancing is one way to control for order effects. Counterbalancing basically means mixing up the order in which tasks are performed in a repeated measures design. So with the experiment above, you might split the participants into two groups. So:–
Group 1 – Sweet condition first, then vitamin condition.
Group 2 – Vitamin condition first, then sweet condition.
So this means that the order effects would be equal across both conditions.
Then any difference should be due to the vitamin (or sweet), rather than the way in which the tasks were performed.