Summary: Introductory Econometrics : A Modern Approach  9780324289787  Jeffrey M Wooldridge
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1 Regression: Multiple
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1.2 Inference

What are the assumptions of OLS? (Gauss markov)
 Linear in parameters (that the betas in linear)
 Random sampling ( violated when data is "selected"
 Sample variation in x (the x's can't be equal)
 ZCM: E(ux)=0. Key to interpret causally. Violated when:
 Omitted variables
 Simultaneity (including reverse causality)
 Measurement error
 Homoscedasticity: The error term has the same variance given any value of x. Var(yx)= sigma squared. If it doesn't hold and Var(ux) does not depend on x, the error term exhibits heteroskedasticity.
 Linear in parameters (that the betas in linear)

What are the steps in empirical economic analysis?
(1) Careful formulation of the question of interest
(2) Formulation of an econometric model
(3) Formulation of hypotheses in terms of unknown model parameters
(4) Data collection and use of econometric methods to estimate the parameters in the econometric model and formally test hypotheses of interest.
(5) Carefully interpret the results. 
What is a good estimator?
Unbiased:
1. expected Beta zero hat = beta zero
2. Expected beta one hat = beta one
Efficient:
1. Smaller variance relative to another one. 
1.3.1 CrossSectional Data

What does crosssectional data mean?
A crosssectional data set consists of a sample of individuals, households, firms, countries, etc taken at a given point in time (through random sampling). 
1.3.2 Time Series Data

What does Time Series Data mean?
A time series data set consists of observations on a variable or several variables over time (GDP, money supply) 
1.3.3 Pooled Cross Sections

What does pooled cross sections mean?
Suchdata have bothcrosssectional data and timeseries features . (Random sampling of households in 1985 with variables like income) 
1.3.4 Panel or Longitudinal Data

What does panel data mean?
A panel data set consists of a time series for each crosssectional member in the data set.
Key distinction with pooled cross sectional data is that the same crosssectional data are followed over a given time period. 
1.4 Causality, Ceteris Paribus, and Counterfactual Reasoning

What is the economist's goal?
The economist's goal is to infer the causal effect of one variable on another.
An association between two or more variables may suggest, but does not establish, a causal effect (correlation does not imply causality)
Ceteris paribus plays a key role in a causal analysis. 
What kind of observational data are there for econometric analysis?
(1) Experimental data for measuring the return to education cannot be obtained (ethical issues, economic costs,..)
(2) Nonexperimental (observational) data on education levels and wages for a large group can be obtained by sampling randomly from the population of working individuals 
2 Time series
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What is a time series?
Data containing measurements of the "same thing" over time. For instance GDP per capita. It allows us to potentially model the dynamics over time. For instance, changes in the past impact future outcomes, short term vs longterm, seasonality and trends.
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Topics related to Summary: Introductory Econometrics : A Modern Approach

Regression: Multiple  Qualitative info & heteroscedasticity

Regression  Deriving the Ordinary Least Squares Estimates

Regression  Properties of OLS on Any Sample Data

Regression  Expected Values and Variances of the OLS estimators

Panel data

Instrumental variables  stage OLS (2SLS)

Instrumental variables  Inference of IV

Instrumental variables  Weak instruments

Multiple Regression Analysis: OLS Asymptotics

Heteroskedasticity

Basic Regression Analysis with Time Series Data  Finite Sample Properties of OLS under Classical Assumptions

Instrumental Variables Estimation and TwoStage Least Squares  Motivation: Omitted Variables in a Simple Regression Model