1、1-1CHAPTER 2Tools of Positive AnalysisCopyright 2010 by the McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill/Irwin2-2The Role of Theory Economic models Virtue of simplicity Judging a model Limitations of models Empirical analysis2-3Causation vs. Correlation Statistical analysis Correlatio

2、n Control group Treatment group Conditions required for government action X to cause societal effect Y X must precede Y X and Y must be correlated Other explanations for any observed correlation must be eliminated2-4Experimental Studies Biased estimates Counterfactual Experimental (or randomized) st

3、udy2-5Conducting an Experimental Study Random assignment to control and treatment groups2-6Pitfalls of Experimental Studies Ethical issues Technical problems Response bias Impact of limited duration of experiment Generalization of results to other populations, settings, and related treatments Black

4、box aspect of experiments2-7Observational Studies Observational study empirical study relying on observed data not obtained from experimental study Sources of observational data Surveys Administrative records Governmental data Econometrics Regression analysis2-8Conducting an Observational Study L =

5、0 + 1wn + 2X1 + + nXn + Dependent variable Independent variables Parameters Stochastic error term Regression analysis Regression line Standard errorwnL0Interceptis 0Slopeis 12-9Types of Data Cross-sectional data Time-series data Panel data2-10Pitfalls of Observational Studies Data collected in non-e

6、xperimental setting Specification issues2-11Quasi-Experimental Studies Quasi-experimental study (= natural experiment) observational study relying on circumstances outside researchers control to mimic random assignment2-12Conducting a Quasi-Experimental Study Difference-in-Difference quasi-experiments Instrumental Variables quasi-experiments Regression-Discontinuity quasi-experiments2-13Pitfalls of Quasi-Experimental Studies Assignment to control and treatment groups may not be ra