Incidence (epidemiology) - Wikipedia
In disease epidemiology, two terms, Incidence and Prevalence, are very much and quite often used. What is (are) the main difference (differences) between. Incidence and prevalence are terms commonly used in describing disease The relationship between incidence and prevalence depends greatly on the. e) The relationships between incidence and prevalence f) Commonly used measures of disease frequency. Measures of effect including: g) Main measures of.
Incidence rates are useful in determining the causality of diseases. This type of measure has not previously been used in MCHP studies, but is starting to be used to define and compare disease specific cohorts e. An illustration A related issue: Measuring the burden of a disease. Issues When calculating incidence and prevalence, make sure that the data individuals are unduplicated during the period of measure. In both incidence and prevalence a clear definition is required for the condition.
Answering the simple questions 'What is a condition?
Incidence and Prevalence
Incident Cases An incident case can be determined based on the first occurrence in the data of a condition e. True incidence is often difficult to get since access to earlier data that might contain an indication of the condition may not be available. Researchers must define a period of time in which to identify new cases. This period of time must be long enough to capture the condition, especially in the case of a rare diseases or diseases with a low rate of diagnosis.
The disease may still be common but the diagnosis may not be made or occur in administrative data unless there is a comorbid or aggravated condition.
Appropriate definition of incidence will be sensitive to the condition being studied. Prevalent Cases Point prevalence - When calculating point prevalence, several years of data can still be used to identify the individuals having a condition.
In this case a single point in time would be used to identify all of those individuals in the cohort that showed the condition at that time.
Principles of Epidemiology | Lesson 3 - Section 2
There are still issues around conditions that are recurrent or of a finite length i. Period prevalence - Along with the issues of 'What' and 'When,' researchers must also answer ' Where '. This is important when using period prevalence since a single individual may have multiple ages and residence locations - even be lost to follow-up.
The time period must also be determined. As with incidence, a long enough period must be used to identify the condition, but not long enough to exaggerate the actual prevalence in the population. A period that is too long will be more affected by mortality and other loss to follow-up issues. Most of the studies involving the occurrence of a disease at MCHP use a measure of period prevalence usually looking over two or three years of data Robinson et al, The primary issues that need to be resolved here are related to changes over time - e.
MCHP researchers have taken several approaches to this problem. The two most common methods for identifying the residence location are: The age and location of residence at the first or incident case in the study. The most frequent residence location, usually RHA or other large area and age that matches the population denominator in the rates measure.
These people did not have HIV at 5 years, but did at 10, so you assume they were infected at 7.
Now take the 50 new cases of HIV, and divide by to get 0. In other words, if you were to follow people for one year, you would see 28 new cases of HIV. This is a much more accurate measure of risk than prevalence. Thus, incidence conveys information about the risk of contracting the disease, whereas prevalence indicates how widespread the disease is.
Prevalence is the proportion of the total number of cases to the total population and is more a measure of the burden of the disease on society with no regard to time at risk or when subjects may have been exposed to a possible risk factor. Prevalence can also be measured with respect to a specific subgroup of a population see: Incidence is usually more useful than prevalence in understanding the disease etiology: For example, consider a disease that takes a long time to cure and was widespread in but dissipated in This disease will have both high incidence and high prevalence inbut in it will have a low incidence yet will continue to have a high prevalence because it takes a long time to cure, so the fraction of individuals that are affected remains high.
In contrast, a disease that has a short duration may have a low prevalence and a high incidence.