In a cohort study we are studying disease X with subtypes A, B, C. When one of these subtypes occurs, the occurrence other subtypes is precluded, therefore I have ran a competing risk regression with competing risk for death and for the other subtypes of the disease.
Now we want to use the cumulative incidence function to estimate the incidence over time. We did this in two different way, namely:
- The normal way. Plot cumulative incidence with time elapsed since start of the first study visit to the end of the study. See figure 1.
- To get an impression of at what age the disease occurs we added elapsed time since beginning of the study to the age of the patient and plotted the cumulative incidence. See figure 2.
I am unsure whether method 2. is a valid method to estimate cumulative incidence at certain ages. If you look at figure 2, you can clearly see that the cumulative incidence for subtype A, B and C is much higher then in figure 1. This is due to lower numbers at risk at high ages (85+ years). It seems to me that this might give misleading representation of the real situation, could someone comment on this methodology?