Perhaps you should try some spelling variations:
observational cohort » observational support, observational errors, observational methods
observational model » observation model, observation models, observations models
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 model ) OR ( observation content ))) OR ( observational cohort )).
• Adding a wildcard symbol may retrieve word variants: (((( observational model ) or ( observation content ))) or ( observational cohort ))*.