A study examining the relationship between humor and memory compares memory performance scores for one group presented with humorous sentences and a second group presented with no humorous sentences. The participants presented with the humorous sentences are all males. The participants presented with the non humorous sentences are all females. In this study, gender (male/female) is best characterized as a(n) variable.

Extraneous

An extraneous variable is a variable in an experiment that you are not intentionally studying. These variables usually provide undesired affects on the experiment.

In this example, the independent variable is whether a sentence is humorous or not, and the dependent variable is the memory performance score. However, because the humorous sentences are only given to males, and the non-humorous sentences are only given to females, gender becomes an extraneous variable as you are not intentionally testing gender's relation to the dependent variable, but it is still affecting the experiment.