No, the function I was referring to was using ‘Observation Period Criteria’ to allow a user to specify an arbitrary start/end date that will be used in the cohort entry events that will result in a user-defined cohort_start_date.
The ‘Add Study Window’ is a function in Incidence Rates which will limit the people included in the calculation if their cohort_start_date is between the study_start and study_end (or just after the study start, if only the study_start date is specified).
This is going to sound confusing but the ‘Study Window’ only does ‘right-side’ censoring, but ‘left side filtering’, meaning: only people where the cohort_start_date between the study_start_date and study_end_date will be included in the analysis. The Time At Risk will not start as based on the study window, it is always based on the cohort_start_date. That’s why I call this ‘left side filtering’. However, if you specify a ‘study_end_date’, it WILL use the study_end date as a ‘time at risk end date’ if the study_end_date occurs before the TAR end. This is why I call it ‘right side censoring’.
I’m a little embarrassed to say that the decision was to do it this way was a matter of simplicity: in order to do complete left censoring properly, you have to account for the cohort_start_date and TAR start adjustment, and it was simpler to just say ‘The only people included are those that cohort_start between the study start and study end’. The study end date is much simpler to handle for censoring: the TAR ends at the earliest of the observation period end date, the study_window end date, or an outcome event date.
However, you can still get the result you want by taking care of the left censoring in the ‘cohort definition’ (that will ‘trim’ the cohort_start dates to a fixed start date), and handle the right censoring using a study window in the IR analysis. In the future, we could work to have this handled completely in the IR Analysis tool, but for now, the simple approach in the IR tool means if you want true ‘left-right censoring’, you will need to censor the cohort_start_dates in the cohort definition, and censor the TAR using the Incidence Rate Study Window setting.
that’s the default behavior of the Cohort Definition: if you don’t specify how a cohort exit date is calculated, by default it uses the containing observation period end date.
The incidence rate doesn’t have a ‘default function’ in this way: part of the Incidence Rate is to define how the Time At Risk is defined based on an offset from the cohort_start_date. These are not optional: you must specify these settings. However, if you also add a study window, it will do the ‘left-filter, right censor’ described above.
Here are some use cases that I’ve seen:
Case 1: 1 year follow up after cohort entry:
TAR Start: cohort_start + 0d, TAR End: cohort_start + 365d
Case 2: During exposure (this assumes cohort_start/end represent the period of continuous exposure
TAR Start: cohort_start + 0d, TAR End: cohort_end + 0d
Case 3: During Exposure with a 30d surveillance window:
TAR Start: cohort_start + 0d, TAR End: cohort_end + 30d
Case 4: 6 months after treatment ends:
TAR Start cohort_end + 0d, TAR END: cohort_end + 183d
Hopefully you see how this all comes together, and how you have to take the meaning of the cohort_start / cohort_end when defining your TAR in the Incidence Rate tool.