Preventive fraction is a ratio where we can calculate a certain value which determines how much of a population is exposed to an external factor, compared to a population which is not exposed. It is usually used to prevent and reduce risks.
It is also referred to as ‘Preventable fraction’ or ‘PF’, which can be derived from relative risk or odds ratio.
It can be calculated as ( 1 − relative risk ) or as ( 1 − odds ratio ).
The procedure to calculate the preventive fraction includes calculation of: Incidence proportions or risks, both in the exposed group and in the non exposed group; relative risk associated with exposure; odds ratio associated with exposure; risk difference with exposure. A 2X2 table is then created. ‘Exposure’ denotes the explanatory variable in the analysis. ‘Risk Ratio’ measures the relative risk associated with exposure. ‘Odds Ratio’ is a type of ‘relative risk’ that is equal to the ‘Risk ratio’ when the outcome is rare.
The concept of preventive fraction is usually used in the fields of medicine, o test the validity of a vaccine, epidemiology, disease prevention and so on.