Thanks a lot @Christian_Reich, this was very helpful. If you do not mind, I have a few follow-up questions.
In fact, I am also struggling to place the disease in one of those three categories. I am interested in sleep apnea, however, since I am looking in the pediatric population, the duration of disease varies quite a lot depending on surgery outcome or patients outgrowing disease. At this point, because I am only looking for a rough estimate, I would go for the simple solution that you are offering here:
However, I am not really clear on how to perform that. Let’s say that I assume disease duration to be around 3 years. Does it mean that I would look at the earliest event any time before the end of the specified 3 year-period? Is this essentially the same as the trivial calculation you have offered for type (iii) diseases, except for a more defined time window? Is there anything else that I would need to perform on Atlas?
At the moment, my aim is to find all people in the database within that specified period in the denominator by using Observation Period. When I look into the number of patients with the disease record within the period of interest, that number is not a true subpopulation of the cohort I create with Observation Period criteria. It captures way more people than when I try to create subgroup analyses on characterizations (which I know is not the right way to go about with the analysis but I wanted to check whether there were major discrepencies). Hence, it would be implied that not everyone that I define as diseased would be a part of the denominator or I believe people would be counted more than once. Do you believe that is an artifact of the approach or is there something that I am essentially wrong about here?
On another point, how do you feel about getting prevalence estimates via incidence rates in a defined period of suspected disease duration? Do you think reliable estimates could be obtained by multiplying the incidence rate with the duration of the disease? I am asking this question as the incidence numbers seem more robust for my analysis using claims data, but I also understand that this might be a stretch.
Thank you very much again, I find Atlas to be a useful tool but I am still trying to get to understand how to best utilize it for different research questions.