Nonrandom Sampling and Tobit Models ECON 721
Different Types of Sampling Random sampling Censored sampling Truncated sampling Nonrandom –Exogenous stratified –Endogenous stratified Choice-based
Tobit Models Main reference: Amemiya, Chapter 10
Type I Tobit Model Tobin’s (1958) example – expenditure on a durable good only observed if expenditure exceeds the minimum price available.
Truncated Type I Tobit Only observe data for people who purchased the good (e.g. gather data at appliance store)
Ways of Estimating Tobit Model MLE If censored, estimating probit and get coefficients up to scale By OLS using results for conditional means of truncated normal random variables
Heckman’s Two-Step Procedure
NLLS
Tobit Type III Model
likelihood
Estimation by MLE
Example: Gronau’s female labor supply model
Heckman’s female labor supply model (explains choice of H as well)
Type III Tobit Model (observe both wages and hours)
Estimation MLE Two-step method
Type V Tobit Model