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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 ]
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.
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 .
Proportionate allocation uses a sampling fraction in each of the strata that are proportional to that of the total population. For instance, if the population consists of n total individuals, m of which are male and f female (and where m + f = n), then the relative size of the two samples (x 1 = m/n males, x 2 = f/n females) should reflect this proportion.
In epidemiology, preventable fraction among the unexposed (PFu), is the proportion of incidents in the unexposed group that could be prevented by exposure.It is calculated as = / =, where is the incidence in the exposed group, is the incidence in the unexposed group, and is the relative risk.
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): = /
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
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.