Pre- and post-test probability: Difference between revisions

Revision as of 04:27, 4 December 2013

Revision as of 14:25, 19 January 2014

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Most major diseases have established [[diagnostic criteria]] and/or [[clinical prediction rule]]s. The establishment of diagnostic criteria or clinical prediction rules consists of a comprehensive evaluation of many tests that are considered important in estimating the probability of a condition of interest, sometimes also including how to divide it into subgroups, and when and how to treat the condition. Such establishment can include usage of predictive values, likelihood ratios as well as relative risks.

For example, the [[Systemic_lupus_erythematosus#Diagnostic_criteria|ACR criteria for systemic lupus erythematosiserythematosus]] defines the diagnosis as presence of at least 4 out of 11 findings, each of which can be regarded as a target value of a test with its own sensitivity and specificity. In this case, there has been evaluation of the tests for these target parameters when used in combination in regard to, for example, interference between them and overlap of target parameters, thereby striving to avoid inaccuracies that could otherwise arise if attempting to calculate the probability of the disease using likelihood ratios of the individual tests. Therefore, if diagnostic criteria have been established for a condition, it is generally most appropriate to interpret any post-test probability for that condition in the context of these criteria.

Also, there are risk assessment tools for estimating the combined risk of several risk factors, such as the online tool [http://hp2010.nhlbihin.net/atpiii/calculator.asp?usertype=prof] from the [[Framingham Heart Study]] for estimating the risk for coronary heart disease outcomes using multiple risk factors, including age, gender, blood lipids, blood pressure and smoking, being much more accurate than multiplying the individual relative risks of each risk factor.