One of the hardest things about being a medical writer is translating medical terms or concepts into words that everybody can understand. As with many other scientific disciplines, jargon or specialized language, permeates the field of medicine. A good medical writer not only understands jargon but also anticipates the needs of the audience--how an audience will best appreciate the medical concepts being discussed.
I decided to write a 3-part blog posting on certain terms that are common in clinical medicine, epidemiology, public health, health psychology and more. The first terms that I will discuss include sensitivity and specificity and incidence and prevalence.
Sensitivity and specificity. According to the AMA Manual of Style, the term sensitivity is defined as "the proportion of individuals with the disease or condition as measured by the criterion standard who have a positive test result. " (The term criterion standard is preferred to the term gold standard and refers to the diagnostic standard for a disease or condition that is used as a basis of comparison for other tests. In other words, the criterion standard is the best test for a disease or condition. Although the AMA Manual of Style defines the terms specificity and sensitivity in terms of the criterion standard, the terms can be applied to any test.) For example, if a test were to have a sensitivity of 99%, then of 100 people who tested positive for the disease, 99 people would actually have the disease.
The AMA Manual of Style defines specificity as "the proportion of those without the disease or condition as measured by the criterion standard who have negative results by the test being studied." For example, if a test were to have a specificity of 99%, then of 100 people who tested negative for the disease, 99 people would actually be disease-free.
Ideally, a good screening test will have a high sensitivity, and a good confirmatory test will have a high specificity. This distinction makes sense, because if you were to screen a large population, you would want to catch as many people with the disease as possible (high sensitivity), and when you were to confirm whether these people have a disease, you would want to weed out as many people as possible (high specificity). Ideally, the criterion standard (gold standard) would have both a high sensitivity and specificity and serve as the best single test for a disease or condition.
Prevalence and incidence. Many people fail to realize that these terms have different meanings. According to the AMA Manual of Style, the term prevalence refers to "the proportion of persons with a particular disease at a given point in time." For example, if the prevalence of a disease were 6.6%, then at any given point in time, there would be 6,600 cases per 100,000 people in a population.
According to the AMA Manual of Style, the term incidence refers to the "number of new cases of disease among persons at risk that occur over time." The period of time is usually a year. For example, if the incidence of a disease were 6.6%, then there would be 6,600 cases per 100,000 people in a population per year. (Presumably, the prevalence of the disease would be higher.)
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