Pre- and post-test probability: Difference between revisions

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{{Use dmy dates|date=August 2013}}

'''Pre-test probability''' and '''post-test probability''' (alternatively spelled pretest and posttest probability) are the [[Subjectivity|subjective]] [[probabilities]] of the presence of a condition (such as a [[disease]]) before and after a [[diagnostic test]], respectively. ''Post-test probability'', in turn, can be ''positive'' or ''negative'', depending on whether the test falls out as a [[positive test]] or a [[negative medical test|negative test]], respectively. In some cases, it is used for the probability of developing the condition of interest in the future.

The subjectivity of the probabilities is based on the fact that, in reality, an individual either has the condition or not (with the probability always being 100%), so pre- and post-test probabilities for individuals can rather be regarded as psychological phenomena in the minds of those involved in the [[diagnostics]] at hand.

Test, in this sense, can refer to any [[medical test]] (but usually in the sense of diagnostic tests), and in a broad sense also including questions and even assumptions (such as assuming that the target individual is a female or male). The ability to make a difference between pre- and post-test probabilities of various conditions is a major factor in the [[Medical test#Indications|indication of medical tests]].

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Additional factors that influence a decision whether a medical test should be performed or not include: cost of the test, availability of additional tests, potential interference with subsequent test (such as an [[abdominal palpation]] potentially inducing intestinal activity whose sounds interfere with a subsequent [[abdominal auscultation]]), time taken for the test or other practical or administrative aspects. Also, even if not beneficial for the individual being tested, the results may be useful for the establishment of statistics in order to improve health care for other individuals.

==Subjectivity==

ThePre- subjectivityand of thepost-test probabilities isare [[Subjectivity|subjective]] based on the fact that, in reality, an individual either has the condition or not (with the probability always being 100%), so pre- and post-test probabilities for individuals can rather be regarded as psychological phenomena in the minds of those involved in the [[diagnostics]] at hand.

==See also==