In diagnostic testing, this refers to the chance of having a negative test result given that you do not have the disease. Specificity of 100% means that all people without the disease will test negative. However, a person could have a negative test result yet still have the disease – 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 people who have a positive test result definitely have the disease. To fully judge the accuracy of a test, its sensitivity must also be considered.