Perhaps you should try some spelling variations:
social effect » social effects, societal effect, special effect
effect model » effect models, effects model, effects models
hats model » charts model, habits model, shafts model
rats model » rat model, rate model, ratio model

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 ((hats model) OR (rats model)) ) OR ( social effect model )).
• Adding a wildcard symbol may retrieve word variants: (( social ((hats model) or (rats model)) ) or ( social effect model ))*.