Those before 1999, I think you can use "approximate method of calculation of incidence rate based on the assumption that they were down with secondary primary malignancy half-way through the study period. For those with full person-years, you will use the "exact method" of calculation since you have the their person-year. So my question is when you said secondary primary malignancy, does that mean lung cancer or you are meant another type of cancer sequel to lung cancer?

Cheers

I presume you are doing indirect standardization by age only, comparing the incidence of any second primary malignancy in those with a diagnosis of lung cancer to the incidence of any primary malignancy in the general population.

You appear to have an identified cohort of lung cancer patients.You know which of the patients developed a second primary after they developed lung cancer.The person years at risk would be calculated from the time of first cancer. The SIR for any second primary would be actual number od second primaries/ expected no of these as a first primay. The expected number would be calculated from the average age specific incidences for the general population over the period 1990-2014.

assuming the general population is quite large (eg national) , the age specific rates for all cancer combined are unlikely to have varied much between 1990 and 1999. So you can use the 1999-2014 general population age specific rates for the whole follow up period 1990-2014.

Hi James Leigh and Babafela Awosile for your answers. I really appreciate you took the time to answer. Babafela Awosile wen I said second primary malignancy I mean all types of cancer together (risk of developing any other cancer in comparison with the general populaton) and by every type of cancer-

James Leigh I will like to ask you a little bit more about your approach (if you have time) . I have attached an excel file:

in "info.all.male" you can observe the person years ( calculated from diagnosis until the end of follow- up ) by year of primary malignancy diagnosis. Below this you will find the age-specific observed cases of second primary malignancies per year in the studied population. Below this you will find the age specific incidence rate per year of the reference population (calculated by the data below this: the age specific cases by year and age specific populations by year).

The next sheet is the calculation of SIR using this information.

If I understood correctly, should I for example use the amount of cases and population from 1999 and repeat it between 1990-1998 so I can get an estimate of the incidence rate for those 24 years or should I just continue using the resulting incidence rate from 1999-2014?

Thank you very much in advance.

Looking at your data it seems that the whole study starts in 1999 . The EXCEL columns have just been shown for 1990 - 1999 as a layout error and the observed case table heading is a labeling error it should be ."observed cases from 1999-2014"

So just follow the procedure from 1999.

note that this is an indirect standardization for both age and calendar period

Is this a course exercise or real data you have ocllected?

Dear James,

Thank you very much for all your help. it is real data that has been collected.