Functionally, they are equivalent: when you add the criteria to the index, you are going to look for the criteria relative to the index's date. When you add the inclusion criteria, you are also applying the inclusion criteria relative to the index events.
However, you can limit the events to earliest per person before applying the inclusion criteria. So, you'd want to put criteria under the index if you want to consider all events before limiting to the first per person. Or if you just want the first index event to be considered for the inclusion criteria, then you'd put your criteria as an inclusion criteria.
Also worth noting: inclusion criteria are applied across all index events that are identified. If you wanted some inclusion criteria to only apply to a specific index event, then you'd apply the criteria at the index event level.
Finally: adding inclusion rules work the same way as the 'initial event inclusion criteria': it takes whatever index events pass the 'earliest/latest' limit + the initial event inclusion criteria' and applies the inclusion rules to the remaining index events such that only index events that pass all inclusion rules are kept in the cohort.
Once you have the final set of index events, we build cohort eras.
So to summarize:
- Add criteria to index when you want these criteria to be applied before limiting to earliest/latest per person.
- Add criteria to index when you want to apply specific criteria to a specific event from index events.
- Add criteria to inclusion criteria when you want to apply criteria to all events from the initial events, or you want to limit index events to 'earliest/latest' first before applying criteria.
-Inclusion Rules are inclusion criteria, but after index criteria and initial inclusion criteria + earliest/latest limits are applied.
I realize that combining all these functions makes it a little hard to understand what is happening, but it was built this way to give some flexibility across use-cases.