Perhaps you should try some spelling variations:
observational concepts » observation concepts, observational conceptual, operational concepts
observational concerns » observational constrains, observational contrains, conservation concerns
observational clues » observational aspects, observational results, observational techniques

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 concepts) OR (observational concerns)))).
• Adding a wildcard symbol may retrieve word variants: ((observational clues) or (((observational concepts) or (observational concerns))))*.