What does specificity mean in statistics?
The specificity of a test (also called the True Negative Rate) is the proportion of people without the disease who will have a negative result. In other words, the specificity of a test refers to how well a test identifies patients who do not have a disease.
What is the specificity of a disease?
The specificity of a test is its ability to designate an individual who does not have a disease as negative. A highly specific test means that there are few false positive results.
How do you calculate specificity of a disease?
The specificity is calculated as the number of non-diseased correctly classified divided by all non-diseased individuals. So 720 true negative results divided by 800, or all non-diseased individuals, times 100, gives us a specificity of 90%.
What sensitivity and specificity is acceptable?
For a test to be useful, sensitivity+specificity should be at least 1.5 (halfway between 1, which is useless, and 2, which is perfect). Prevalence critically affects predictive values. The lower the pretest probability of a condition, the lower the predictive values.
How do you interpret specificity?
Specificity is the proportion of people WITHOUT Disease X that have a NEGATIVE blood test. A test that is 100% specific means all healthy individuals are correctly identified as healthy, i.e. there are no false positives.
What does a specificity of 50% mean?
Specificity: From the 50 healthy people, the test has correctly pointed out all 50. Therefore, its specificity is 50 divided by 50 or 100%. According to these statistical characteristics, this test is not suitable for screening purposes; but it is suited for the final confirmation of a disease.
What is a good specificity number?
A positive result in a test with high specificity is useful for ruling in disease. The test rarely gives positive results in healthy patients. A test with 100% specificity will recognize all patients without the disease by testing negative, so a positive test result would definitely rule in the presence of the disease.
What is specificity in epidemiology?
What does specificity mean in health?
(SPEH-sih-FIH-sih-tee) When referring to a medical test, specificity refers to the percentage of people who test negative for a specific disease among a group of people who do not have the disease. No test is 100% specific because some people who do not have the disease will test positive for it (false positive).
How is the sensitivity and specificity of a disease determined?
After getting the numbers of true positives, false positives, true negatives, and false negatives, the sensitivity and specificity for the test can be calculated. If it turns out that the sensitivity is high then any person who has the disease is likely to be classified as positive by the test.
What is the specificity of a blood test?
The test misses one-third of the people who have disease. The test has 53% specificity. In other words, 45 persons out of 85 persons with negative results are truly negative and 40 individuals test positive for a disease which they do not have.
What does it mean when a test has high specificity?
Likewise, high specificity — when a test does a good job of ruling out people who don’t have the disease – usually means that the test has lower sensitivity (more false-negatives).
When does the specificity of a screening test decrease?
A specific test is usually negative in disease free patients (few false positives ). When many disease free patients have a positive test (false positives), the specificity decreases. Utility as a screening test may diminish because it results in too many needless work-ups.