Perhaps you should try some spelling variations:
product model » production model
rabbit model » rabbit hole
probit model » probit models, robust model
tobit model » probit models
logit model » logit models, logic model, logistic 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: ((((((tobit model) OR (rabbit model))) OR (((probit model) OR (product model))))) OR (logit model)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((((tobit model) OR (rabbit model))) or (((probit model) or (product model))))) or (logit model))".
• Adding a wildcard symbol may retrieve word variants: ((((((tobit model) OR (rabbit model))) or (((probit model) or (product model))))) or (logit model))*.