Mehdi,

How did you calculate the age-specific incidence rate? What data analysis package are you using?

Usually, you calculate the incidence by dividing the number of failures (CRC cases) by the person-time. Person time is the "time at risk" that all participants contributed to your study data. You can calculate this by adding up the time your subjects contributed until the failure.

STATA has a command for this, "stsptime". It will do the calculations for you.

Here are 2 links that can help you:

https://sph.unc.edu/files/2015/07/nciph_ERIC4.pdf

https://www.stata.com/manuals13/ststptime.pdf

Roberto J. Vidri Thank you. Actually, I have new cases of each year (for example 2005-2006) for all childhood cancers in my country. This data consists all new cases of the country over 10 years during 2005-2014. Now I now all new cases during 10 years (for each group of age such as 0-4, 5-9, 10-15, 15-19) and I know the total population of 10 years (for each group of age such as 0-4, 5-9, 10-15, 15-19). The weights used to calculate the age standardized rate is also based on Segi. Now I want to know. is this way correct?

Dear Mehdi

To calculate average annual incidence rate (single value for the six years), there is a simple method

1. You add all cases registered in the six years and obtain their average

Summation of cases in 10 years

Average number of cases =---------------------------------------------------------= A

6

2. Obtain the mid-period population by either similar method to 1 above or

just take the average of the population in the middle two years ( population of 2007 +population of 2008) divided by two = B

A

The average annual incidence rate =--------------- X100000

B

With best regards