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Data organization
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Regression Models Time series Cross-sectional Panel Multi-dimensional panel
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Errors in Uni-dimensional Data
In standard time series or cross-sectional data sets, we must adjust for non-independent errors. Serial correlation Errors correlated across time Spatial correlation Errors correlated across cross-sections Heteroskedasticity Error variance changes over time or cross-sections
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Errors in Panel Data Heterogeneous serial correlation Errors correlated across time and differently for different cross-sections. Heterogeneous spatial correlation Errors correlated across cross-sections but differently for different time periods. Heterogeneous heteroskedasticity Error variance changes over time, but does so differently for different cross-sections. Serial-spatial correlation Past errors from one cross-section are correlated with future errors from a different cross-section.
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Generalized Least Squares
The error covariance matrix shows the covariances of error terms across different observations.
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Ordinary Least Squares Assumptions
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Ordinary Least Squares (Heteroskedasticity)
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Ordinary Least Squares (Serial Correlation)
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Two-Dimensional Panel Data: OLS Assumptions
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Two-Dimensional Panel Data: OLS Assumptions
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Two-Dimensional Panel Data: OLS (homogeneous serial correlation)
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Two-Dimensional Panel Data: OLS (heterogeneous serial correlation)
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Two-Dimensional Panel Data: OLS (serial-spatial correlation)
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OLS vs. Panel Estimation
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Fixed versus Random Effects
Under the random effects assumption, and are treated as stochastic. Under the fixed effects assumption, they are treated as fixed in repeated samples.
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Random vs. Fixed Effects
Random Effects Assumption Pro: Estimators are more efficient Con: Estimators are inconsistent if any of the three errors are not IIN(0,σ2) across all dimensions. Fixed Effects Assumption Pro: Estimators are consistent regardless of and . Con: Estimators are less efficient. See Hausman test for endogeneity.
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Random vs. Fixed Cross-Sectional Effects
Test statistic = 22
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Alternatives to Panel Techniques
Separate Regressions Drawbacks Less efficient estimators due to lost information about cross-sectional error covariance. Remove the ability to restrict parameter values across cross-sections.
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Alternatives to Panel Techniques
Pooled Regression Drawbacks Less efficient estimators due to lost information about cross-sectional error covariance. Restricts parameter values to be equal across cross-sections.
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Alternatives to Panel Techniques
Pooled Regression with Cross-Sectional Dummies Drawbacks This is the fixed effects panel technique. If the cross-sectional dummies are IIN, then parameter estimates are less efficient than under the random effects panel technique.
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Procedures to use with panel data
Generalized least squares (GLS) Generalized method of moments (GMM) OLS with “automated” corrections for serial correlation, etc. is GLS.
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Extra stuff Panel data reveals information that is unattainable with non-panel data.
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Three-Dimensional Structure of the ASA-NBER Data Set
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Shock Occurrence vs. Shock Impact
These shocks all impact inflation in quarter 9 but occur in different quarters. These shocks all occur in quarter 6 but impact inflation in different quarters.
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Cross-sectional shocks
Shock Occurrence vs. Shock Impact Cumulative shocks Cross-sectional shocks Discrete shocks
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Shock Occurrence vs. Shock Impact
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