Sometimes in psychology experiments, groups of participants are required to take the same test more than once. In some cases, performance can change from the first instance of testing and the next simply due to repeating the activity.
Definition: A practice effect is any change that results merely from the repetition of a task.
What Are Practice Effects?
In an experiment looking at the impact of sleep deprivation on driving ability, for example, students might take a driving test at the beginning of the experiment and again at the end of the experiment. Participating in the first task may influence how well students do on the second task.
Such effects are often a concern in experiments that use a within-subjects design. Any type of repeated measure design is susceptible to possible practice effects.
Practice effects can also impact test performance on standardized testing and psychological assessments. Taking the same test a second time soon may lead to better scores or altered performance.
These effects do not always lead to improvements, however. Sometimes practice effects can help future performance, but they can also hinder subsequent performance on experimental tasks or tests.
How to Avoid Practice Effects
One way of controlling the impact of practice is through counterbalancing. The experiments will vary the order in which treatments are given to subjects, which might involve using randomization or utilizing all possible treatment orders.
While counterbalancing does not eliminate the effects of practice, it does allow researchers to see if such practice effects are present, how they interact with the independent variables, and if other steps need to be taken to correct the experimental design.
Carryover Effects
Carryover effects are a type of practice effect in which the results from one test influences how a person does on the next test. This can happen in a few different ways:
Interference
Learning on the first task might interfere with performance on a second task. For example, participants in a memory experiment might memorize a list of words for one task. When asked to memorize words in a second task, the words they learned in the first part of the experiment might interfere with their performance on the second memory task.
Revealing Experimental Purpose
Another type of carryover effect can occur if the first task somehow makes the participant aware of the purpose of the experiment. If the participants know (or think they know) what the experiment is about, they might alter their behavior or performance on subsequent tasks.
Impact of Practice Effects
While practice effects are usually viewed as sources of error in testing and research, in some cases they may actually be useful.
For example, researchers have found that individuals with mild cognitive impairment do not show practice effect improvements when tested on the same material repeatedly, where those without cognitive impairments do.
Such findings suggest that the absence of practice effects might have diagnostic value in some instances.
Sources:
Duff K, Beglinger L, Schultz S, et al. Practice effects in the prediction of long-term cognitive outcome in three patient samples: A novel prognostic index. Archives of Clinical Neuropsychology. 2007;22(1):15-24. doi:10.1016/j.acn.2006.08.013