Equivalence is the quality or state of being alike or having the same function. Applied to psychological testing, test equivalence refers to assessment tools that measure similar constructs equally well and thus can be used interchangeably. Equivalent or interchangeable test forms are of great use in psychological assessment. For instance, there are several circumstances in which an individual might be given the same assessment multiple times, such as before and after psychotherapy, before and after a surgery or other medical intervention, or to track changes due to age, disease, trauma, or other circumstance. This entry discusses practice effects, other reasons for testing for equivalence, cultural and linguistic considerations for test designers, and the use of alternative forms.

Unfortunately, a number of tests have known practice effects. ...