Perhaps you should try some spelling variations:
observational concepts » observation concepts, observational concerns, observational conceptual
observational cohort » observational support, observational methods, observational method
observational errors » observational methods, observational method, observational clues
observational cinema » observational clinical, observational context, observational economy

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 errors))) OR (observational cinema))) OR (observational concepts)).
• Adding a wildcard symbol may retrieve word variants: ((((((observational cohort) or (observational errors))) or (observational cinema))) or (observational concepts))*.