# Econometric Analysis of Panel Data

## Presentation on theme: "Econometric Analysis of Panel Data"— Presentation transcript:

Econometric Analysis of Panel Data
William Greene Department of Economics Stern School of Business

Dear Professor Greene, I have to apply multiplicative heteroscedastic models, that I studied in your book, to the analysis of trade data. Since I have not found any Matlab implementations, I am starting to write the method from scratch. I was wondering if you are aware of reliable implementations in Matlab or any other language, which I can use as a reference.

a “multi-level” modelling feature along the following lines
a “multi-level” modelling feature along the following lines? My data has a “two level” hierarchical structure: I'd like to perform an ordered probit analysis such that we allow for random effects pertaining to individuals and the organisations they work for.

-----------------------------------------------------------------------------
Random Coefficients  OrdProbs Model Dependent variable                 HSAT Log likelihood function     Estimation based on N =    947, K =  14 Inf.Cr.AIC  =   AIC/N =    3.951 Unbalanced panel has    250 individuals Ordered probit (normal) model LHS variable = values 0,1,...,10 Simulation based on    200 Halton draws         |                  Standard            Prob.      95% Confidence     HSAT|  Coefficient       Error       z    |z|>Z*         Interval         |Nonrandom parameters Constant|    ***          16.05  .0000             AGE|    ***           .0000            EDUC|     ***           4.33  .0000                  |Scale parameters for dists. of random parameters Constant|    ***          27.57  .0000                 |Standard Deviations of Random Effects R.E.(01)|     *             1.71  .0877                 |Threshold parameters for probabilities   Mu(01)|     **            2.53  .0113            ... Mu(09)|    ***          39.20  .0000

Agenda Single equation instrumental variable estimation Panel data
Exogeneity Instrumental Variable (IV) Estimation Two Stage Least Squares (2SLS) Generalized Method of Moments (GMM) Panel data Fixed effects Hausman and Taylor’s formulation Application Arellano/Bond/Bover framework

Structure and Regression

Exogeneity

An Experimental Treatment Effect

Instrumental Variables
Instrumental variable associated with changes in x, not with ε dy/dx = β dx/dx + dε /dx = β + dε /dx. Second term is not 0. dy/dz = β dx/dz + dε /dz. The second term is 0. β =cov(y,z)/cov(x,z) This is the “IV estimator” Example: Corporate earnings in year t Earnings(t) = β R&D(t) + ε(t) R&D(t) responds directly to Earnings(t) thus ε(t) A likely valid instrumental variable would be R&D(t-1) which probably does not respond to current year shocks to earnings.

Least Squares

The IV Estimator

A Moment Based Estimator

Cornwell and Rupert Data
Cornwell and Rupert Returns to Schooling Data, 595 Individuals, 7 Years Variables in the file are EXP = work experience, EXPSQ = EXP2 WKS = weeks worked OCC = occupation, 1 if blue collar, IND = 1 if manufacturing industry SOUTH = 1 if resides in south SMSA = 1 if resides in a city (SMSA) MS = 1 if married FEM = 1 if female UNION = 1 if wage set by unioin contract ED = years of education LWAGE = log of wage = dependent variable in regressions These data were analyzed in Cornwell, C. and Rupert, P., "Efficient Estimation with Panel Data: An Empirical Comparison of Instrumental Variable Estimators," Journal of Applied Econometrics, 3, 1988, pp  See Baltagi, page 122 for further analysis.  The data were downloaded from the website for Baltagi's text.

Wage Equation with Endogenous Weeks
logWage=β1+ β2 Exp + β3 ExpSq + β4OCC + β5 South + β6 SMSA + β7 WKS + ε Weeks worked is believed to be endogenous in this equation. We use the Marital Status dummy variable MS as an exogenous variable. Wooldridge Condition (5.3) Cov[MS, ε] = 0 is assumed. Auxiliary regression: For MS to be a ‘valid’ instrumental variable, In the regression of WKS on [1,EXP,EXPSQ,OCC,South,SMSA,MS, ] MS significantly “explains” WKS. A projection interpretation: In the projection XitK =θ1 x1it + θ2 x2it + … + θK-1 xK-1,it + θK zit , θK ≠ 0. (One normally doesn’t “check” the variables in this fashion.

Auxiliary Projection | Ordinary least squares regression | | LHS=WKS Mean = | |Variable | Coefficient | Standard Error |b/St.Er.|P[|Z|>z] | Mean of X| Constant EXP EXPSQ OCC SOUTH SMSA MS

Application: IV for WKS in Rupert
| Ordinary least squares regression | | Residuals Sum of squares = | | Fit R-squared = | | Adjusted R-squared = | |Variable | Coefficient | Standard Error |b/St.Er.|P[|Z|>z] | Constant EXP EXPSQ D OCC SOUTH SMSA WKS

Application: IV for wks in Rupert
| LHS=LWAGE Mean = | | Standard deviation = | | Residuals Sum of squares = | | Standard error of e = | | Fit R-squared = | | Adjusted R-squared = | | Not using OLS or no constant. Rsqd & F may be < 0. | |Variable | Coefficient | Standard Error |b/St.Er.|P[|Z|>z] | Constant EXP EXPSQ D OCC SOUTH SMSA WKS OLS WKS

Generalizing the IV Estimator-1

Generalizing the IV Estimator - 2

Generalizing the IV Estimator

The Best Set of Instruments

Two Stage Least Squares

2SLS Estimator

2SLS Algebra

A General Result for IV We defined a class of IV estimators by the set of variables The minimum variance (most efficient) member in this class is 2SLS (Brundy and Jorgenson(1971)) (rediscovered JW, 2000, p )

GMM Estimation – Orthogonality Conditions

GMM Estimation - 1

GMM Estimation - 2

IV Estimation

An Optimal Weighting Matrix

The GMM Estimator

GMM Estimation

Application - GMM NAMELIST ; x = one,exp,expsq,occ,south,smsa,wks\$
NAMELIST ; z = one,exp,expsq,occ,south,smsa,ms,union,ed\$ 2SLS ; lhs = lwage ; RHS = X ; INST = Z \$ NLSQ ; fcn = lwage-b1'x ; labels = b1,b2,b3,b4,b5,b6,b7 ; start = b ; inst = Z ; pds = 0\$

Application - 2SLS

GMM Estimates

2SLS GMM with Heteroscedasticity

Testing the Overidentifying Restrictions

Specification Test Based on the Criterion

Extending the Form of the GMM Estimator to Nonlinear Models

A Nonlinear Conditional Mean

Nonlinear Regression/GMM
NAMELIST ; x = one,exp,expsq,occ,south,smsa,wks\$ NAMELIST ; z = one,exp,expsq,occ,south,smsa,ms,union,ed\$ ? Get initial values to use for optimal weighting matrix NLSQ ; lhs = lwage ; fcn=exp(b1'x) ; inst = z ; labels=b1,b2,b3,b4,b5,b6,b7 ; start=7_0\$ ? GMM using previous estimates to compute weighting matrix NLSQ (GMM) ; fcn = lwage-exp(b1'x) ; inst = Z ; labels = b1,b2,b3,b4,b5,b6,b7 ; start = b ; pds = 0 \$ (Means use White style estimator)

Nonlinear Wage Equation Estimates NLSQ Initial Values

Nonlinear Wage Equation Estimates 2nd Step GMM

IV for Panel Data