# How do you interpret population etiologic fractions?

## How do you interpret population etiologic fractions?

PAF is defined as the fraction of all cases of a particular disease or other adverse condition in a population that is attributable to a specific exposure; PAF equals (O − E)/O, where O and E refer to the observed number of cases and the expected number of cases under no exposure, respectively.

## What is the etiologic fraction of disease?

Excess fractions measure the number of excess cases of disease due to a specific exposure of interest. Etiologic fractions measure the number of cases of disease due to a specific exposure of interest.

How do you calculate attributable fractions in epidemiology?

Attributable Proportion Among the Exposed It is calculated by taking the risk difference, dividing it by the incidence in the exposed group, and then multiplying it by 100 to convert it into a percentage.

### Is the fraction of the population *?

Attributable fraction for the population combines both the relative risk of an incident with respect to the factor, as well as the prevalence of the factor in the population. In such case, removal of the risk factor will greatly reduce the number of the incidents in the population.

### Why population attributable fractions can sum to more than one?

PAFs can sum to more than 1 because some individuals with more than one risk factor can have disease prevented in more than one way, and the prevented cases of these individuals could be counted more than once.

How do you find prevented fractions?

The prevented fraction is computed by subtracting the disease risk in individuals with the intervention measure (for example, an anti-leprosy vaccine) from the disease risk in individuals without the intervention, and expressing the difference as a proportion of the latter.

## How do you find the etiologic fraction?

Etiologic fraction = [ a / ( a + b ) − c / ( c + d ) ] 1 − [ c / ( c + d ) ] (population attributable risk). The relative risk used by epidemiologists for prospective studies differs slightly from the odds ratio used in case–control studies and is defined as a/(ac)/b(bd).

## How do you find preventive fractions?

What is population harvesting?

An Introduction to Population Ecology – Harvesting a Population with Logistic Growth. Harvesting can represent reduction of the population due to hunting or capturing individuals, which in effect removes individuals from the population (Edwards & Penney, 1999).

### What is constant harvesting?

There are two standard approaches to harvesting from a population. We can harvest a set number of individuals every time (constant harvesting), or we can harvest a set percentage of the population every time (proportional harvesting).