Perhaps you should try some spelling variations:
observational context » observational concepts, observational contacts, observationsin contexts
observational cohort » observational support, observational errors, observational methods
observation content » observation concept, observation consistent, observation concepts

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: ((observational cohort) OR (((observational context) OR (observation content)))).
• Adding a wildcard symbol may retrieve word variants: ((observational cohort) or (((observational context) or (observation content))))*.