Perhaps you should try some spelling variations:
observational conceptual » observation conceptual, conservation conceptual, observation concept
observational concepts » observation concepts, observational concerns, operational concepts
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) OR (observational conceptual)))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((((observational cohort) or (observational errors))) or (observational cinema))) or (((observational concepts) OR (observational conceptual))))".
• Adding a wildcard symbol may retrieve word variants: ((((((observational cohort) or (observational errors))) or (observational cinema))) or (((observational concepts) OR (observational conceptual))))*.