I was looking at creating cohorts in Atlas section from
Book of OHDSI and have few questions. I also refered few posts in forum on cohort exit as well. can I confirm my understanding of the below items?
I understand cohort exit can be done using 3 ways.
1) End of continuous observation
Ex: A person is in cohort as long as his observation period ends. Simple and straight forward. Irrespective of break in his records for drugs or labs etc he will still be in the cohort. Let’s say subject XYZ has observation period start date as 1/1/2001 and observation period end date as 31/12/2005. So his cohort end date will be 31/12/2005. Right?
2) Fixed duration relative to an event
a) Let’s say subject 123 entered the cohort on 1st Jan 2010 for Hypertension condition or started on Metformin medication. I add 10 days as offset to his initial event (which is Hypertension condition/Metformin medication). So am I right to understand that he will leave the cohort on 11th Jan 2010? But what’s the use in increasing/decreasing/restricting the cohort duration of the patients?
b) Does adding zero days as offset is same as “end of continuous observation”? I know it throws a warning to have no of days to offset as greater than 0
c) Does setting a date offset will help us retain only record per person? Why to restrict his cohort duration?
3) End of continuous drug exposure
a) Should this field be used only if we consider anything related to drugs as Initial events?
For ex: Subject named “Jack” has calcium acetate drug records from 1st Dec 2009 to 12 Dec 2009. Then he again has same calcium acetate records from 27th Dec 2009 to 11th Jan 2010.
I understand if we mention a gap of 30 days, his cohort end date will become 11th Jan 2010. Because it collapses the 2 drug episodes into an era. Am I right?
For ex: Subject named “John” has Metformin from Feb 1st 2010 to Feb 23rd 2010. Then he again has it on 27th Feb 2010 to Mar 15th 2010.
In this case, let’s say I allow maximum window of “0” zero days. So will his cohort end date become Feb 23rd 2010?
But why do we have to pick “Drug concept set” again when we have already defined it in the initial event? Will it not be able to look at it? Because we get the cohort start date from initial events.
I might be wrong here. aren’t we almost always interested in the number of people who satisfy the cohort criteria?. Once I get the list of subjects who satisfy the criteria to enter the cohort, I would anyway be looking at their other data domains to get their corresponding baseline features. How does it matter for us to know how long they were in cohort or when they leave the cohort?
Any simple explanation would really be helpful