Sensitivity and specificity:
Used in relation to laboratory tests, radiological examinations, clinical signs and symptoms.
Sensitivity – True positives. Expressed as the number of positives who have the disease divided by the total with the disease x 100 – a sensitive test has a high proportion of true case
– How good the test is at picking up those with the disease.
Specificity – True negatives. Expressed as the number of negatives who do not have the disease divided by the number without the disease x 100 – a specific test has few false positives
– How good is the test at excluding those without the disease
A good test will detect most people with the disease (high sensitivity) and exclude most people without the disorder (high specificity).
Likelihood ratio – how much more likely a positive test is to be found in someone with, as opposed to someone without the disease.
The likelihood of a positive test = sensitivity/(1-specificty)
The likelihood of a negative test = (1-sensitivity)/specificity