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Identification in Probit Model. In most probit models, the index function is linear in its parameters, so that and cannot be separately identified. Typically normalize . Logit Model. The standard logit model results if the errors are iid extreme value variates, with . This in turn yields .
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1. Probit
2. Identification in Probit Model
3. Logit Model
4. Identification in the Logit Model
5. Estimation:Nonlinear Least Squares
6. Maximum Likelihood
7. Maximum Likelihood (cont’d)
8. Maximum Likelihood (cont’d)
9. Maximum Likelihood (cont’d)
10. Maximum Likelihood (cont’d)
11. Maximum Likelihood Given that you have specified your model correctly, the resulting parameter estimates will be
consistent estimates of the true parameters
efficient (i.e., lowest variance)
asymptotically normal
12. Inference in Discrete Choice Models
13. Fitted Choice Probabilities Issues
What are the statistical properties of fitted choice probabilities?
How does one aggregate over decision makers to make inference for the population?
14. Taylor Series Expansion
15. Taylor Series Expansion(cont’d)
16. Simulation
17. Example: Chicago Transit Authority Explanatory variables
TW: walking time from nearest train stop to place of work (+)
AIVTSS: Difference between drive time and train ride time (-)
ACF: Difference between auto-parking charge and train fare (-)
AW: Number of vehicles in the household (+)
18. Estimated Parameters (MLE)
19. Fitted Choice Probabilities
20. Aggregation
21. Train (2002) Example
23. Errors in Aggregation
24. Sample Enumeration In aggregating over individuals or projecting to the population as a whole, one needs to keep in mind
Degree to which sample is representative of target population
Endogeneities in sample selection
Sample enumeration frequently used when sample is exogeneously determined
Controlling for endogenous sampling is more difficult
25. Sample Enumeration (cont’d)
26. Marginal Effects
27. Marginal Effects – Logit
28. Marginal Effects Continued
30. Logit and Probit Yield Similar Results
31. Example #1: Greene
33. For Transportation Study:Marginal Effects