I was trying to replicate an example from Knol et al (Knol 2012, Int J Epidemiol, Recommendations for presenting analyses of effect modification and interaction) but I dont get the same results as the authors, who give the following example data (part of table 2):
In the unexposed group (chronic disease score = 0) there are 243 cases (diabetes) and 24195 controls (no diabetes).
In the exposed group (chronic disease score > 0) there are 338 cases (diabetes) and 11260 controls (no diabetes).
So the risk in exposed = 338/(338+11260) = 0.029
Risk in unexposed = 243/(243+24195) = 0.0099
RR = 0.029 / 0.0099 = 2.9
Yet the authors provide an RR of 1.55 and I cannot grasp how they arrived at that figure.