What do each of the following represent?
(a) The proportion of persons who test positive for some disease who actually have the disease.
(b) The proportion of persons with some disease that test positive for the disease.
(c) The proportion of persons who do not have some disease who test negative for the disease.
(d) The proportion of persons who test negative for some disease who do not have the disease.
To understand what each of the following represents, let's break down the meaning of each phrase:
(a) The proportion of persons who test positive for some disease who actually have the disease.
This represents the concept of "accuracy" or "true positive rate." It refers to the proportion of individuals who test positive for a specific disease and, indeed, have the disease. In other words, it measures how well a positive test result corresponds to the presence of the disease in reality.
To calculate this proportion, you would need the number of individuals who tested positive for the disease and were confirmed to have it. This can be obtained by comparing test results with a reference standard, such as a gold standard diagnostic test or medical evaluation.
(b) The proportion of persons with some disease that test positive for the disease.
This represents the concept of "sensitivity" or "true positive rate." It refers to the proportion of individuals who have a particular disease and test positive for it. It measures how effectively a test can correctly identify individuals with the disease.
To calculate this proportion, you would need the number of individuals who have the disease and test positive for it. This information can be obtained by conducting tests or by cross-referencing with known cases of the disease.
(c) The proportion of persons who do not have some disease who test negative for the disease.
This represents the concept of "specificity" or "true negative rate." It refers to the proportion of individuals who do not have a specific disease and test negative for it. It measures how accurately a test can identify individuals who do not have the disease.
To calculate this proportion, you would need the number of individuals without the disease who test negative for it. This information can be obtained by conducting tests on individuals who are known not to have the disease or by comparing test results with a reference standard.
(d) The proportion of persons who test negative for some disease who do not have the disease.
This represents the concept of "accuracy" or "true negative rate." It refers to the proportion of individuals who test negative for a specific disease and, indeed, do not have the disease. It measures how well a negative test result corresponds to the absence of the disease in reality.
To calculate this proportion, you would need the number of individuals who tested negative for the disease and were confirmed to be disease-free. Similar to case (a), this information can be obtained by comparing test results with a reference standard or proper medical evaluation.
Understanding these different proportions helps evaluate the performance and reliability of diagnostic tests and their ability to correctly identify the presence or absence of a disease.