Because I do want to have the index date as the cohort start date, I tried specifying the cohort definition that way - see public ATLAS here
n on STRIDE ~ 6600
I found I had to create my own concept set for inpatient visit, creating a visit criteria (which defaults to any Visit) and then specifying inpatient visit as a criteria attribute didn't seem to work.
But compare (1) with (2):
So a big difference in sample size, the two are not equivalent. But then I presume the cohort index date in (2) is that of the procedure occurrence, not the inpatient visit as I'm looking for.
You raise another point though - and that's the short term window. I had acutally assumed that if the long term window was set the medium and short term where redundant - i.e. that these are overlapping sets.
The way the params are organized suggests the same:
longTermDays = 365, mediumTermDays = 180,shortTermDays = 30,windowEndDays =0
i.e. they all have the same windowEndDays argument.
So currently I actually have set UseCovariateXXXXMedium and Short terms to false. I will dig into the documentation - but are these non overlapping sets?
Patrick (in an email thread) suggested I change windowEndDays to -1. Have done that, still get suspiciously good performance. I will try to manually impose a longer washout, but obviously the preference here is a cohort definition that takes the visit start date as the index date, from which I can subtract one day to ensure a clean set of predictors.