OHDSI Home | Forums | Wiki | Github

Continous observation vs.observation period

Hello, it might be a simple question… but I’m just curious about the difference between ‘continuous observation’ and ‘observation period’ when I’m designing cohort in cohort definition tab.

It would be great if anyone can answer my question! Thanks :slight_smile:

@yeorim Sorry but I cannot understand what you mean exactly. If you’re Korean, could you replicate it in Korean and describe the details?

유승찬 선생님 안녕하세요, 에비드넷 안여림입니다.

제가 궁금했던 것은 코호트 디자인 시 위 두 개념이 어떤 차이가 있는 것이었습니다!

Luckily, I’m in the vicinity of @yeorim, so after meeting her in the real world, I explained the above problem.

1 Like

Thanks for explaining to me face-to-face!! :grinning:

For anyone who is also faced with this question, I will try to explain the concepts/difference:

Observation Periods indicate the period of time (indicated with a start and end date) where it is possible for a person to have observed events. In Health Claims context, this would be enrollment because a health plan won’t have records of care if you haven’t been enrolled with the plan (how would they know you exist?).

Continuous observation means that between 2 points in time, there is no gap in the observation period, or the two points in time is completely contained inside a single observation period.

When searching for cohort entry events in cohort definition, you have the option to specify ‘prior continuous observation’ and ‘post continuous observation’, which means: at the time of the entry event, is there continuous observation between X days before the entry event start date (prior) or Y days after the entry event start date (post). So, Observation period have a set calendar start-end, and continuous observation is determned by taking the entry event start date, and making another calendar period based on start - prior days and start. If start-prior to start falls within the observation period, then the prior days is ‘continuous’.

Why do you want to enforce ‘continuous’? For cases where you want to say something like ‘there is no observation of N in the prior 180 days’, you should require that there is actually 180 days of prior continuous observation. If you don’t, then you will determine that a person with 0 days of prior observation didn’t have an exclusion event, but if they don’t have the actual prior observation, you can’t actually make that determination.

Other cases is looking for people with a minimum amount of follow up: if you require ‘post continuous observation’, then that means that the person is still within an observation period for at least the number of post-observation days. This is helpful when you want to do a study and you need to observe the person in data for at least 180 days: you set the post-continuous observation to 180.