# cumulative incidence formula

If you are using an Excel spreadsheet, you could calculate the CI using the formula: In the graph below the upper blue line shows the predicted number of deaths using the approximation CI = IR x T. The lower line, in red, shows the more accurate projection of cumulative deaths using the exponential equation. Find compound growth rate from cumulative totals, Seemingly very confusing question about a stream of payments with changing structure over time. Or outcif? Why do these angles look weird in my logo? Why is it wrong to answer a question with a tautology? Cumulative incidence Incidence proportion is the proportion of an initially disease-free population that develops disease, becomes injured, or dies during a specified (usually limited) period of time. rev 2020.11.11.37991, The best answers are voted up and rise to the top, Mathematics Stack Exchange works best with JavaScript enabled, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, Learn more about hiring developers or posting ads with us. Need further help from the community? The advantage here is, as you noted, to convert back to a percentage is almost obvious. Cumulative incidence is calculated by the number of new cases during a period divided by the number of subjects at risk in the population at the beginning of the study. Can you translate the things you just said in terms of an equation or adding a step in your equation from above?. Incidence rate is therefore more analogous to the speed of a car, which is typically expressed in miles per hour. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. How to solve this problem without the assistance of a calculator in under 3 minutes? sign in and ask a new question. Hope it helps. To learn more, see our tips on writing great answers. Cumulative incidence (CI) and incidence rate (IR) are different approaches to calculating incidence, based on the nature of followup time. of disease onsets ≅ N⋅∆t Prevalence = no. How to find rate of depreciation in this problem? An incidence rate is less intuitive, because it is really an estimate of the instantaneous rate of disease, i.e. The integral I j(t) = Z t 0 f j(u)du= PrfT tand J= jg is called the cumulative incidence function (CIF), and represents the prob- By following your steps the percentage is directly calculated as follows $\%Inflation=\frac{15.5}{100}x100=15.5\%$ Is this reasoning correct?. Because all the numbers "look the same" it is not easy to get the picture. The freq Freq does not seem to work on my SAS 9.4. 4/ Cumulative inflation over 2 mounth = 10% of B + 5.5% of B = 15.5% of B. Now my other problem is that it does not give me the expected results when I calulate it by. Examine the METHODS option. The equation above would lead us to believe that after 50 years the cumulative incidence of death would be CI = IR X T = 11 X 50 = 550 deaths in a population which initially had 1,000 members. In reality, there would only be 423 deaths after 50 years. @ChrisSteinbeckBell I've added a formula and some more explanation. By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. It only takes a minute to sign up. 1) 100 USD at the beginning of September. Which part is not correct in my interpretation?. I was wondering whether someone could help me with the SAS code to directly compute the cumulative incidence and survival probability (over the course of follow-up). Total price increase in % for the combined period? I do not know how to get it in proc lifetest or the other procedures you mentioned. So there is an adjustment to be made. your calculation is fine. Thanks for contributing an answer to Mathematics Stack Exchange! When I calculate it manually, I get Survival =.0.46 and cumulative incidence=0.54 (i.e. How to calcuate the cumulative incidence and the survival probability, Re: How to calcuate the cumulative incidence and the survival probability, I will take anything that can compute it for me. of new cases of disease or injury / Size of population at risk x 100. Cumulative Incidence = No. I am just wondering whether I am making a mistake in my SAS code. Where the period of time considered is an entire lifetime, the incidence proportion is called lifetime risk. Number of people who develop the disease in a specified time period / Number of people at risk of developing the disease at the start of the period. Are you sure you want proc phreg and not proc lifetest? Not necessary !!!! At first glance it would seem logical that, if the incidence rate remained constant the cumulative incidence would be equal to the incidence rate times time: This relationship would hold true if the population were infinitely large, but in a finite population this approximation becomes increasingly inaccurate over time, because the size of the population at risk declines over time. The calculation is $(1+0.1)\times (1+0.05)=1.155=1+0.155$, So if the cost of goods at the beginning of September is $C$ and the inflation rate for September is $i_S \%$, then the cost of those same goods at the end of September is $$C+\frac {i_S}{100}C=\left(1+\frac {i_S}{100}\right)C$$, Now the cost of goods at the beginning of October is $\left(1+\frac {i_S}{100}\right)C$ and if inflation duding October is $i_O\%$ the same logic applies and the price at the end of October is $$\left(1+\frac {i_O}{100}\right)\left(1+\frac {i_S}{100}\right)C$$ When I calculate it manually, I get Survival =.0.46 and cumulative incidence=0.54 (i.e. (105 +10.5) USD = 115.5 USD, I.e 5% inflation in October. Join us on November 19 to learn what's new with the program.