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Positivity Criterion and Cutoff Values

Although medical professionals use the terms positive and negative to describe the results of diagnostic tests, many tests produce results along a continuum (e.g., millimeters of ST-segment depression in an exercise stress test, brain natriuretic peptide level for making the diagnosis of decompensated congestive heart failure). For such tests, a criterion must be established for defining a result as being either positive or negative. This cut-point, or cutoff value, is called a positivity criterion.

Selection

Although for many tests, positivity criteria have been selected based on the variation observed in a population of apparently normal individuals (e.g., mean ±2 standard deviations) encompassing 95% of the population, such a definition may not be optimal for clinical purposes. Ideally, the choice of a positivity criterion should consider the ...

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