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The relationship between incidence (rate), point prevalence (ratio) and period prevalence (ratio) is easily explained via an analogy with photography. Point prevalence is akin to a flashlit photograph: what is happening at this instant frozen in time.
When the incidence is approximately constant for the duration of the disease, prevalence is approximately the product of disease incidence and average disease duration, so prevalence = incidence × duration. The importance of this equation is in the relation between prevalence and incidence; for example, when the incidence increases, then the ...
Epidemiology has its limits at the point where an inference is made that the relationship between an agent and a disease is causal (general causation) and where the magnitude of excess risk attributed to the agent has been determined; that is, epidemiology addresses whether an agent can cause disease, not whether an agent did cause a specific ...
Epidemiological (and other observational) studies typically highlight associations between exposures and outcomes, rather than causation. While some consider this a limitation of observational research, epidemiological models of causation (e.g. Bradford Hill criteria) [7] contend that an entire body of evidence is needed before determining if an association is truly causal. [8]
In epidemiology and actuarial science, the term morbidity (also morbidity rate or morbidity frequency) can refer to either the incidence rate, the prevalence of a disease or medical condition, or the percentage of people who experience a given condition within a given timeframe (e.g., 20% of people will get influenza in a year). [18]
Note that the PPV is not intrinsic to the test—it depends also on the prevalence. [2] Due to the large effect of prevalence upon predictive values, a standardized approach has been proposed, where the PPV is normalized to a prevalence of 50%. [11] PPV is directly proportional [dubious – discuss] to the prevalence of the disease or condition ...
Sensitivity and specificity are prevalence-independent test characteristics, as their values are intrinsic to the test and do not depend on the disease prevalence in the population of interest. [6] Positive and negative predictive values , but not sensitivity or specificity, are values influenced by the prevalence of disease in the population ...
Epidemiology is the study of the distribution and determinants of diseases and other health states in populations. Epidemiological studies can be divided into two main types: [citation needed] Descriptive epidemiology describes disease and/or exposure and may consist of calculating rates, e.g., incidence and prevalence.