Perhaps you should try some spelling variations:
observational economy » observational astronomy, observational cinema, observational errors
observational cohort » observational support, observational errors, observational methods
observation content » observation concept, observation consistent, observational context

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 economy) OR (observational cohort))) OR (observation content)).
• Adding a wildcard symbol may retrieve word variants: ((((observational economy) or (observational cohort))) or (observation content))*.