how to calculate incidence rates
in order to calculate the incidence rate of a particular event take the number of new instances of the event in question disease illness accident financial event during a specific period of time and divide that by the total population at risk during that period of time 21 experts must determine the length of time and this time period must be long enough to allow a detailed study 2the result is generally presented as a number of cases in a certain amount of the population it s important to make sure that no information is duplicated in order to get as much of an accurate determination of the rate 2let s say that experts want to determine the incidence rate of foreclosure in anytown u s the total number of homeowners in town is 10 000 experts undertake the study for a full year and learn the number of new foreclosures is 200 using the formula above they determine that the incidence rate of foreclosure in anytown is 0 02 examples of incidence ratelet s say a county in the u s with a population of 500 000 may have had 20 new cases of tuberculosis in 2013 this translates to an incidence rate of four cases per 100 000 persons this is higher than the incidence rate of tb for the entire u s 9 852 new tb cases in 2013 for an incidence rate of three cases per 100 000 persons now let s take a look at an example to determine trends using incidence rates consider a study on lung cancer rates released in january 2014 by the centers for disease control and prevention the study found that thanks to tobacco control efforts lung cancer incidence rates from 2005 to 2009 declined by 2 6 per year among men from 87 to 78 cases per 100 000 men the lung cancer incidence rate for women fell 1 1 per year from 57 to 54 cases per 100 000 women incidence vs prevalenceincidence should not be confused with prevalence remember that incidence measures the likelihood of occurrence during a specific time period prevalence on the other hand is a measure of the actual number of cases of a condition or illness in a population at a certain point in time therefore it is the total accumulation of incidences over a period of time 1here s an example to show how the two terms are distinct the incidence of loan foreclosures would be the number of foreclosed loans over a time period prevalence would be the total number or all of the incidences added up while incidence enables an assessment to be made of the risk of contracting a disease prevalence shows whether the disease is widespread or not the incidence rate can be further categorized by different characteristics such as race gender or age incidence rates and market researchincidence rates are commonly used by the food and drug administration fda to determine if and when pharmaceutical companies are allowed to take their drugs to market in order to do so these companies are required to conduct clinical trials over a series of phases and apply for fda clearance to determine the efficacy of their drugs 3companies enlist individuals to take part in studies these people are given the drug or a placebo during each phase according to the fda the reviewer should identify the subset of trials in phase 2 and 3 databases that will provide the best estimate of rates and develop tables of event rates based on that judgment in order to determine the incidence rate of any adverse side effects 3 these findings are presented in tables that are reported to the fda incidence rates show the rate at which reactions take place along with the severity of each one 4companies rely on positive results and approval in order to get their drugs to market which is usually a long drawn out process meeting these goals means good news for investors especially if the results are really positive but those that aren t able to achieve these milestones often see their stocks drop these losses can be offset if drug companies are undertaking other positive trials or if they have products on the market 