Specificity

In diagnostic testing, this refers to the chance of having a negative test result given that you do not have the disease. A 100% specificity means that those without the disease will test negative but this is not the same the other way round. A patient could have a negative test result but still have the disease or condition – this is called a false negative. The specificity of a test is also related to its positive predictive value (true positives) – a test with a specificity of 100% means that all those who get a positive test result definitely have the disease or condition. To fully judge the accuracy of a test, its sensitivity must also be considered.