Dr. Wickersham wants to examine how light affects participants' performance on a counting task. So she has two groups, one that works under dim light and one that works under bright lights. She finds that those in the dim-light condition perform better. However, one of her research assistants admits that he gave those in the dim-light condition extra time to complete the task. Now Dr. Wickersham is not sure whether those in the dim-light condition did better because of the lighting or because of the extra time they received. The extra time on the test is an example of a(n) _____ variable.

Extraneous variable: In psychology, the term "extraneous variable" is determined as a variable that can directly affects an experiment's results irrespective of being an independent variable. However, in any experiment a researcher or an experimenter isn't purposely studying extraneous variable, and is often considered as an "undesirable variable".

In the question above, the extra time on the test is an example of an extraneous variable.