Metaphorically, a "gold standard" is a highly-valued and well-accepted instance of a class against which other such instances can be compared.

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In psychology and medicine, a treatment that is designated the "gold standard" is not necessarily the best treatment, but it is one that has been around a long time, intensively studied, and is relatively well-understood. Experimental treatments can then be compared to it, as well as to placebo, in order to determine their effectiveness and usefulness in comparison to existing therapies and to each other.

For example, many studies of antidepressant medication or psychotherapy still use imipramine, an old tricyclic antidepressant as their gold standard. While the SSRIs are generally thought to be better, imipramine has been used much more extensively and offers a common basis of comparison among studies.