Quality criterias for a diagnostic test

<p>The figure illustrates <strong>the quality criteria for a diagnostic test</strong>:</p> <ul> <li>Sensitivity and specificity as pre-probability before the test is used in routine practice</li> <li>Positive and negative predictive value as post-probability interpretation of the result&nbsp;</li> </ul> <p><strong>A diagnostic test</strong> is a diagnostic tool with a binary output, i.e. yes/no, sick/healthy, suitable/unsuitable or positive/negative.&nbsp;</p> <p><strong>Explanation</strong></p> <p>Before being used in diagnostics or screening, the two parameters of the diagnostic test <strong>sensitivity </strong>and <strong>specificity </strong>are determined. This is done on (known) sick or infected and healthy or non-infected persons. In the case of sick persons, the statistical measures of true-positive and false-positive are also obtained. In the case of healthy persons, the statistical measures true-negative and false-negative are also obtained.</p> <p>After the test has been performed, <strong>the positive predictive value</strong> indicates the probability that, if the test result is positive, the person is actually sick or infected (post-test probability).</p> <p>After the test has been carried out, <strong>the negative predictive value</strong> indicates the probability that, in the case of a negative test result, the person is actually healthy or non-infected (post-test probability).</p>