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 effective model"
"special effects model" » "special effects models", "special effect models"
"social exact model" » "social etats model", "social et model", "social email model"

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"social exact model\") OR (\"social effect model\"))) OR (\"special effects model\"))".
• Removing quotes may allow a broader search: (((( social exact model ) OR ( social effect model ))) OR ( special effects model )).
• Adding a wildcard symbol may retrieve word variants: (((("social exact model") OR ("social effect model"))) OR ("special effects model"))*.