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(共14张PPT)
TOOLS OF POSITIVE ANALYSIS
Chapter 2
Public Finance and Positive Analysis
One goal of Public Finance is to estimate how government policy affects individuals’ behavior.
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The Role of Theory
Economic models
Provide frameworks for thinking about the factors that might influence behavior.
Generate hypotheses whose validity can be assessed through empirical work.
Virtue of simplicity: reduces a problem to its essentials.
Empirical analysis: Analysis based on observation and experience.
Used to test hypotheses.
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Causation vs. Correlation
Conditions required for government action X to cause societal effect Y rather than just correlate (move together) with effect Y.
X must precede Y
X and Y must be correlated
Other explanations for any observed correlation must be eliminated
The importance of the distinction for policy.
Example: There is a positive correlation between being married and wages…Does that mean government should enact a policy encouraging marriage as a way of increasing wages
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Empirical Work:
Experimental Studies
Experimental (or randomized) study: subjects are randomly assigned to either a treatment group or control group.
Treatment Group: Group of people who are subject to the intervention being studied.
Control Group: Comparison group of people who are not subject to the intervention being studied.
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Empirical Work:
Experimental Studies
Randomization improves the chances that the control and treatment groups have similar characteristics
Focus can then be on possible causation between treatment and outcome.
Randomization has a large potential to eliminate biased estimates.
Biased estimate: conflates the true causal impact with the impact of outside factors.
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Pitfalls 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 box aspect of experiments
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Empirical Work:
Observational Studies
Observational study – empirical study relying on observed data not obtained from experimental study
Sources of observational data
Surveys
Administrative records
Governmental data
Econometrics: statistical techniques to establish and estimate causal relationships in absence of randomization.
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Conducting Observational Studies
Estimating Relationships
L = α0 + α1wn + α2X1 + … + αnXn + ε
Dependent variable
Independent variables
Parameters
Stochastic error term
Regression analysis
Regression line:
Best fit through scatter of data
Standard error
Indicates reliability of equation
wn
L
α0
Intercept is α0
Slope is α1
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Empirical Work:
Types of Observational Study Data
Cross-sectional data: contains information on individual entities at a given point in time.
Time-series data: contains information on a single entity at different points in time.
Panel (longitudinal) data: combines features of both.
Contains information on individual entities at different points in time.
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Pitfalls of Observational Studies
Data collected in non-experimental setting
Difficult to ensure that the control group forms a valid “counterfactual”
Counterfactual: the outcome for people in the treatment group had they not been treated.
Specification issues – Not all variables that should be included are available in dataset and/or cannot be measured.
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Empirical Work
Quasi-Experimental Studies
Quasi-experimental study (natural experiment) – observational study relying on circumstances outside researcher’s control to mimic random assignment
Successful Quasi-Experiments hinge on ensuring the treatment group assignment is random.
Difference-in-Difference Quasi-Experiments.
Instrumental Variables Quasi-Experiments
Regression-Discontinuity Quasi-Experiments
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Pitfalls of Quasi-Experimental Studies
Assignment to control and treatment groups may not be random
Not applicable to all research questions
Generalization of results to other settings and treatments might not be possible.
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Chapter 2 Summary
Economic theory provides a framework for analyzing the causal relationship between government policy and individuals’ behavior.
Empirical work tests hypothesis arising from economic theory to determine if it is consistent with real-world phenomena.
Various methods for conducting empirical work exist.
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