For most tests a negative result is not always obtained when there is no disease. Some patients will have a positive result, even if no disease is present. These are therefore, **false positives**, as the test is incorrect.

Equally for most tests a positive result is not always obtained when there is disease. Some cases have a negative result, even if disease is present. These are therefore, **false negatives**, as the test is incorrect.

Positive test results are a sum of the true positive and false positive results.

Negative test results are a sum of the true negative and false negative results.