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In epidemiology, attributable fraction among the exposed (AF e) is the proportion of incidents in the exposed group that are attributable to the risk factor. The term attributable risk percent among the exposed is used if the fraction is expressed as a percentage. [ 1 ]
Equivalently it can be calculated as = + (), where is the exposed proportion of the population and is the relative risk not adjusted for confounders. [ 1 ] [ 2 ] It is used when an exposure increases the risk, as opposed to reducing it, in which case its symmetrical notion is preventable fraction for the population .
In epidemiology, preventable fraction for the population (PFp), is the proportion of incidents in the population that could be prevented by exposing the whole population.. It is calculated as = /, where is the incidence in the exposed group, is the incidence in the populati
Lifetime prevalence (LTP) is the proportion of individuals in a population that at some point in their life (up to the time of assessment) have experienced a "case" (e.g., a disease, a traumatic event, or, a behavior, such as committing a crime). Often, a 12-month prevalence (or some other type of "period prevalence") is provided in conjunction ...
Incidence should not be confused with prevalence, which is the proportion of cases in the population at a given time rather than rate of occurrence of new cases. Thus, incidence conveys information about the risk of contracting the disease, whereas prevalence indicates how widespread the disease is.
The formula for calculating the NEPP is = where N = population size,; P d = prevalence of the disease,; P e = proportion eligible for treatment,; r u = risk of the event of interest in the untreated group or baseline risk over appropriate time period (this can be multiplied by life expectancy to produce life-years),
To determine an appropriate sample size n for estimating proportions, the equation below can be solved, where W represents the desired width of the confidence interval. The resulting sample size formula, is often applied with a conservative estimate of p (e.g., 0.5): = /
This expression has limitations concerning the susceptibility proportion, e.g. the R 0 equals 0.5 implicates S has to be 2, however this proportion exceeds the population size. [citation needed] Assume the rectangular stationary age distribution and let also the ages of infection have the same distribution for each birth year.