In medicine and psychology, clinical significance is the practical importance of a treatment effect—whether it has a real genuine, palpable, noticeable effect on daily life.
[2] A level of significance is selected (most commonly α = 0.05 or 0.01), which signifies the probability of incorrectly rejecting a true null hypothesis.
In terms of testing clinical treatments, practical significance optimally yields quantified information about the importance of a finding, using metrics such as effect size, number needed to treat (NNT), and preventive fraction.
[6] Effect size can provide important information about the results of a study, and are recommended for inclusion in addition to statistical significance.
[5] This technical use within psychology and psychotherapy not only results from a carefully drawn precision and particularity of language, but it enables a shift in perspective from group effects to the specifics of change(s) within an individual.
[citation needed] In contrast, when used as a technical term within psychology and psychotherapy, clinical significance yields information on whether a treatment was effective enough to change a patient's diagnostic label.
It is very possible to have a treatment that yields a significant difference and medium or large effect sizes, but does not move a patient from dysfunctional to functional.
[citation needed] Within psychology and psychotherapy, clinical significance was first proposed by Jacobson, Follette, and Revenstorf[9] as a way to answer the question, is a therapy or treatment effective enough such that a client does not meet the criteria for a diagnosis?
Additionally, clinicians look for information in the assessment data and the client's history that corroborates the relevance of the statistical difference, to establish the connection between performance on the specific test and the individual's more general functioning.