How to calculate P value for incidence rate

[Dearbhla Kelly]

Hello,

I have calculated the crude incidence rates per 1000 population per year of strokes in patients with and without kidney disease e.g.18.37 (16.94-19.9) vs 6.37 (5.78-7.0). How do I calculate the p value for difference?

Thanks!

[Carlo Lazzaro]

I would consider -poisson-.