Introduction

Diagnosis is an essential step in medical care. Usually this involves ‘diagnostic tests’ of some description. A health check is also a group of diagnostic tests. Decisions about medical treatment are made on the basis of test results.

If disease is present an ideal, or truly accurate, test will always give a positive result, whilst if disease is not present, the test will always give a negative result. This is not the case for all tests. The properties of the test that tell us about test accuracy are called sensitivity and specificity.

Sensitivity is defined as the proportion of people with disease who have a positive test result. Specificity is defined as the proportion of people without disease who have a negative test result.