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The attack rate is calculated as the number of people who became ill divided by the number of people at risk for the illness. In order to calculate an attack rate, a case definition, or set of criteria to define the disease of interest, must first be developed.
Definition of incidence rate. Incidence rate or person-time rate is a measure of incidence that incorporates time directly into the denominator. A person-time rate is generally calculated from a long-term cohort follow-up study, wherein enrollees are followed over time and the occurrence of new cases of disease is documented.
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Attack rate. In epidemiology, the attack rate is the proportion of an at-risk population that contracts the disease during a specified time interval. [1] It is used in hypothetical predictions and during actual outbreaks of disease. An at-risk population is defined as one that has no immunity to the attacking pathogen, which can be either a ...
Attack rate is a term used in epidemiology, usually in the setting of outbreaks, to define the risk of contracting a disease during a specified period (i.e. outbreak duration). The overall attack rate refers to the total number of new cases divided by the total population:
- Introduction
- Learning Objectives
- 'Population'
- Ratios, Proportions, and Rates
- Prevalence
- Incidence: Risk, Cumulative Incidence (Incidence Proportion), and Incidence Rate
- Incidence Rate
- Relationship of Incidence Rate to Cumulative Incidence
- Life Tables and Survival Analysis
- Relationship Among Prevalence, Incidence Rate, and Average Duration of Disease
For centuries, knowledge about the cause of disease and how to treat or prevent it was limited by the fact that it was based almost entirely on anecdotal evidence. Significant advances occurred when the strategy for studying disease shifted to looking at groupsof people and using a numeric approach to make critical comparisons.
After successfully completing this section, the student will be able to: 1. Define what is meant by the term 'population' in both descriptive epidemiology and analytic epidemiology. 2. Explain the difference between fixed versus dynamic populations. 3. Explain the differences among the parameters: ratio, proportion, & rate. 4. Define and calculate ...
A population is simply a group of people with some common characteristic, such as age, race, gender, or place of residence. A "target population" is a population for which you would like to make some conclusions. Examples: 1. residents of Mumbai 2. members of Blue Cross/Blue Shield (a U.S. health insurance organization) 3. postmenopausal women in M...
Ratio: A ratio is just a number that is obtained by dividing one number by another. A ratio doesn't necessarily imply any particular relationship between the numerator and the denominator. For example, if there were 100 women in this class and 20 men, the ratio of women to men would be 100/20 or 5 women for each man. This is just a simple ratio tha...
The measure of disease frequency we have calculated is the prevalence, that is, the proportion of the population that has disease at a particular time. Prevalence indicates the probability that a member of the population hasa given condition at a point in time. It is, therefore, a way of assessing the overall burden of disease in the population, so...
In contrast to prevalence, incidence is a measure of the occurrence of new cases of disease (or some other outcome) during a span of time. There are two related measures that are used in this regard: incidence proportion (cumulative incidence) and incidence rate. A useful way to think about cumulative incidence (incidence proportion) is that it is ...
Remember that a rate almost always contains a dimension of time. Therefore, the incidence rate is a measure of the number of new cases ("incidence") per unit of time ("rate"). Compare this to the cumulative incidence (incidence proportion), which measures the number of new cases per person in the population over a defined period of time. Because st...
Cumulative incidence (the proportion of a population at risk that will develop an outcome in a given period of time) provides a measure of risk, and it is an intuitive way to think about possible health outcomes. An incidence rate is less intuitive, because it is really an estimate of the instantaneous rate of disease, i.e. the rate at which new ca...
(Optional) The equation CI = IR x T provides a reasonable estimate of risk when the incidence rate is relatively constant, but this isn't always the case. When the incidence rate changes over time there are other options for estimating risk. 1. One could calculate risk serially over shorter time intervals during which risk is reasonably constant. H...
Prevalence is the proportion of a population that has a condition at a specific time, but the prevalence will be influenced by both the rate at which new cases are occurring and the average duration of the disease. Incidence reflects the rate at which new cases of disease are being added to the population (and becoming prevalent cases). Average dur...
Jul 28, 2009 · After that the attack rate in each of the groups is calculated using the formula for attack rate given above. The next step is to find a difference in attack rates between the two groups. The food or drink items which show the biggest differences in attack rates can be responsible for an outbreak of disease (Friis and Sellers 2004).
Definition of risk ratio. A risk ratio (RR), also called relative risk, compares the risk of a health event (disease, injury, risk factor, or death) among one group with the risk among another group. It does so by dividing the risk (incidence proportion, attack rate) in group 1 by the risk (incidence proportion, attack rate) in group 2.
