Estimation of Pre- and Post-test Probability
Further information: Pre- and post-test probabilityThe likelihood ratio of a test provides a way to estimate the pre- and post-test probabilities of having a condition.
With pre-test probability and likelihood ratio given, then, the post-test probabilities can be calculated by the following three steps:
- Pretest odds = (Pretest probability / (1 - Pretest probability)
- Posttest odds = Pretest odds * Likelihood ratio
In equation above, positive post-test probability is calculated using the likelihood ratio positive, and the negative post-test probability is calculated using the likelihood ratio negative.
- Posttest probability = Posttest odds / (Posttest odds + 1)
In fact, post-test probability, as estimated from the likelihood ratio and pre-test probability, is generally more accurate than if estimated from the positive predictive value of the test, if the tested individual has a different pre-test probability than what is the prevalence of that condition in the population.
Read more about this topic: Likelihood Ratios In Diagnostic Testing
Famous quotes containing the words estimation, pre- and/or probability:
“... it would be impossible for women to stand in higher estimation than they do here. The deference that is paid to them at all times and in all places has often occasioned me as much surprise as pleasure.”
—Frances Wright (1795–1852)
“... he held it one of the prettiest attitudes of the feminine mind to adore a man’s pre- eminence without too precise a knowledge of what it consisted in.”
—George Eliot [Mary Ann (or Marian)
“Only in Britain could it be thought a defect to be “too clever by half.” The probability is that too many people are too stupid by three-quarters.”
—John Major (b. 1943)