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Posted 12-30-2021 01:27 AM
(952 views)

Hi everyone,

I am trying to calculate the standardised incidence ratio using event rates observed in a cohort of patients during our study and comparing that to expected rates in the background population of an outcome.

The data file can be loaded using the code below, and contains age group (in 5 years intervals), follow up time in the study per age group expressed as person-year, the number of events observed in our study, and finally, the expected rates of the event of interest in the background population (these numbers are taken from the Australian Bureau of Statistics).

```
data Study;
infile cards dlm=" ";
input AgeGroup PersonYear ObservedEvents ExpectedRate;
datalines;
0 3.187542779 0 0.0000010000
5 17.83367557 0 0.0000010000
10 105.2190281 0 0.0000000000
15 228.3169062 0 0.0000010000
20 345.8637919 1 0.0000011667
25 347.238193 2 0.0000010000
30 325.2368241 0 0.0000015714
35 289.4476386 5 0.0000030323
40 217.0006845 2 0.0000056774
45 237.1403149 0 0.0000133548
50 268.3819302 3 0.0000255161
55 296.0999316 3 0.0000468065
60 228.3620808 2 0.0000705806
65 166.2388775 3 0.0001121935
70 90.23819302 1 0.0001589355
75 49.30732375 0 0.0002208065
80 23.21560575 2 0.0002692903
85 10.38877481 0 0.0003176452
;
run;
```

Basically, you can use the follow-up time in person-year and multiply it by the expected event rate to get the number of expected events in the study population, and from there calculate the standardised incidence ratio using the approach described here:

https://epiville.ccnmtl.columbia.edu/interactive/sir.html

However, doing this manual calculation has a number of disadvantages, such as not (directly) getting the 95% confidence intervals and p-value .

I have been doing some reading including experimenting with proc stdrate, but I cannot figure out how to use proc stdrate on my dataset. From what I understand you need follow up time and events in the background population (rather than the rates) to calculate SIR.

I am quite stuck here, I cannot get the population number/ age distribution data for Australia to use in my calculation. I wonder if anyone could please assist in implementing stdrate or any other SAS procedure to calculate SIR from the table above?

Thank you.

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Thanks @StatDave worked fine

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