Perhaps you should try some spelling variations:
"social effect model" » "social effects model", "societal effect model", "special effect model", "social effect models", "social effects models"
"social exact model" » "social etats model", "social et model", "social email model"
"social rats model" » "social rates model", "social rate model", "social etats model", "social rat model", "social ratio model"

Try widening your search to All Fields.

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: (((("social exact model") OR ("social effect model"))) OR ("social rats model")).
• Removing quotes may allow a broader search: (((( social exact model ) or ( social effect model ))) or ( social rats model )).
• Adding a wildcard symbol may retrieve word variants: (((("social exact model") or ("social effect model"))) or ("social rats model"))*.