Perhaps you should try some spelling variations:
social effect » social effects, societal effect, special effect
effect model » effect models, effects model, effects models
etats model » etas model, beats model, hats model
rats model » rate model, ratio model, parts model
rats » rates
rat » rate

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 ((etats model) OR (((rats model) OR (rat model)))) ) OR ( social effect model )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( social ((etats model) or (((rats model) OR (rat model)))) ) or ( social effect model ))".
• Adding a wildcard symbol may retrieve word variants: (( social ((etats model) or (((rats model) OR (rat model)))) ) or ( social effect model ))*.