Perhaps you should try some spelling variations:
observational economy » observational astronomy, observational cinema, observational coding
observational context » observational concepts, observational contacts, observation content
observational cohort » observational support, observational methods, observational method
observational errors » observational methods, observational method, observational clues

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 economy))) OR (observational context)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((((observational cohort) OR (observational errors))) or (observational economy))) or (observational context))".
• Adding a wildcard symbol may retrieve word variants: ((((((observational cohort) OR (observational errors))) or (observational economy))) or (observational context))*.