Perhaps you should try some spelling variations:
observational techniques » interventional techniques, computational techniques
observational context » observational concepts, observational contacts, observation content
observational clues » observational aspects, observational results, observational errors

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