Πέμπτη 16 Νοεμβρίου 2017

Sensitivity is not enough. Response to: Postoperative delirium portends descent to dementia

Editor—I welcome the thoughtful discussion by Aranake-Chrisinger & Avidan about testing for postoperative cognitive decline.1 However, the penultimate paragraph is potentially misleading because it makes two common statistical errors. Firstly, there is confusion about the meaning and importance of test sensitivity. In addition to sensitivity, a test's utility needs to be evaluated in the context of its specificity and the disease prevalence. A test with 99% sensitivity can be clinically useless if it has poor specificity, or is used in a low prevalence population.23 Their equating of a 50% sensitivity with a 50% positive predictive value is another commonly made mistake. The SNOUT (negative result in a sensitive test rules out the disease) acronym is unhelpful for the same reasons. Secondly, the article states that repetition of a test can help its sensitivity. This is only true if repeated testing produces results with some degree of conditional independence.4 There is no benefit from repeated testing if keeps giving the same result.

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