Relationship between specificity and sensitivity of a test

Sensitivity and specificity - Wikipedia

relationship between specificity and sensitivity of a test

Sensitivity is the probability that a test will indicate 'disease' among those with the relationship between disease prevalence and predictive value in a test with. Unlike sensitivity and specificity, predictive values vary with the prevalence of a The NLR is the ratio between the false negative and true negative rates and. I read that sensitivity is inversely related to specificity as used in ROC curves. question, there is usually a tradeoff between sensitivity of the test and specificity.

Sensitivity, specificity, and other terms The following terms are fundamental to understanding the utility of clinical tests: When evaluating a clinical test, the terms sensitivity and specificity are used. The terms positive predictive value PPV and negative predictive value NPV are used when considering the value of a test to a clinician and are dependent on the prevalence of the disease in the population of interest.

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Sensitivity The sensitivity of a clinical test refers to the ability of the test to correctly identify those patients with the disease. A high sensitivity is clearly important where the test is used to identify a serious but treatable disease e.

Screening the female population by cervical smear testing is a sensitive test.

Sensitivity and Specificity

However, it is not very specific and a high proportion of women with a positive cervical smear who go on to have a colposcopy are ultimately found to have no underlying pathology. Specificity The specificity of a clinical test refers to the ability of the test to correctly identify those patients without the disease. As discussed above, a test with a high sensitivity but low specificity results in many patients who are disease free being told of the possibility that they have the disease and are then subject to further investigation.

In this way, nearly all of the false positives may be correctly identified as disease negative.

relationship between specificity and sensitivity of a test

Positive predictive value The PPV of a test is a proportion that is useful to clinicians since it answers the question: This is defined as how much more likely is it that a patient who tests positive has the disease compared with one who tests negative. Consider the following example: However, if a patient has signs of SLE e.

Understanding and using sensitivity, specificity and predictive values

We may also consider a woman who presents with breathlessness post-partum and where one of the differential diagnoses is pulmonary embolism.

A D-dimer test would almost certainly be elevated in this patient population; therefore, the test has a low PPV for pulmonary embolism.

relationship between specificity and sensitivity of a test

However, it has a high NPV for pulmonary embolism since a low D-dimer is unlikely to be associated with pulmonary embolism. Screening this population would therefore yield true positives and true negatives with 20 patients being tested positive when they in fact are well and 20 patients testing negative when they are ill.

Sensitivity and specificity

This discussion highlights the fact that the ability to make a diagnosis or screen for a condition depends both on the discriminatory value of the test and on the prevalence of the disease in the population of interest. Receiver operator characteristic curves Consider the following hypothetical example: A sample of SpRs is tested before the examination resulting in a range of endorphin values.

How to calculate Sensitivity and Specificity

However, it is important to point out that none of these are definitive; they raise a heightened suspicion of disease, but they aren't diagnostic. A definitive diagnosis generally requires more extensive, sometimes invasive, and more reliable evaluations. Nevertheless, let's return to the PSA test as an example of a screening test.

relationship between specificity and sensitivity of a test

In the absence of disease, levels of PSA are low, but elevated PSA levels can occur in the presence of prostate cancer, benign prostatic enlargement a common condition in older menand in the presence of infection or inflammation of the prostate gland. Thus, elevated levels of PSA may help identify men with prostate cancer, but they do not provide a definitive diagnosis, which requires biopsies of the prostate gland, in which tissue is sampled by a surgical procedure or by inserting a needle into the gland.

Understanding and using sensitivity, specificity and predictive values

The biopsy is then examined by a pathologist under a microscope, and based on the appearance of cells in the biopsy, a judgment is made as to whether the patient has prostate cancer or not.

Obviously, if the screening test is to be useful clinically two conditions must be met.

relationship between specificity and sensitivity of a test

First, the test has to provide an advantage in distinguishing between, for example, men with and without prostate cancer. Second, one needs to demonstrate that early identification and treatment of the disease results in some improvement: One can collect data to examine the ability of a screening procedure to identify individuals with a disease.