<P> Accuracy is also used as a statistical measure of how well a binary classification test correctly identifies or excludes a condition . That is, the accuracy is the proportion of true results (both true positives and true negatives) among the total number of cases examined . To make the context clear by the semantics, it is often referred to as the "Rand accuracy" or "Rand index". It is a parameter of the test . </P> <P> In psychometrics and psychophysics, the term accuracy is interchangeably used with validity and constant error . Precision is a synonym for reliability and variable error . The validity of a measurement instrument or psychological test is established through experiment or correlation with behavior . Reliability is established with a variety of statistical techniques, classically through an internal consistency test like Cronbach's alpha to ensure sets of related questions have related responses, and then comparison of those related question between reference and target population . </P> <P> In logic simulation, a common mistake in evaluation of accurate models is to compare a logic simulation model to a transistor circuit simulation model . This is a comparison of differences in precision, not accuracy . Precision is measured with respect to detail and accuracy is measured with respect to reality . </P> <Table> <Tr> <Td> </Td> <Td> This section may be confusing or unclear to readers . Please help us clarify the section . There might be a discussion about this on the talk page . (March 2013) (Learn how and when to remove this template message) </Td> </Tr> </Table>

Standard deviation a measure of accuracy or precision