Why Use Instrumental Variables? e Instrumental Variables(IV)estimation is used when your model has endogenous xs That is, whenever Cov(x,l)≠0 Thus. i can be used to address the problem of omitted variable bias 2 Additionally iv can be used to solve the classic errors-in-variables problem Economics 20- Prof anderson

A True panel vs a Pooled cross section Often loosely use the term panel data to refer to any data set that has both a cross sectional dimension and a time-series dimension More precisely it's only data following the same cross-section units over time Otherwise it's a pooled cross-section Economics 20- Prof anderson

Functional form e We' ve seen that a linear regression can really fit nonlinear relationships 2 Can use logs on RHS, LHS or both Can use quadratic forms ofx's Can use interactions ofx's e How do we know if we've gotten the right functional form for our model? Economics 20- Prof anderson

Redefining variables Changing the scale of the y variable will lead to a corresponding change in the scale of the coefficients and standard errors. so no change in the significance or interpretation Changing the scale of one x variable will lead to a change in the scale of that coefficient and standard error, so no change in the significance or interpretation Economics 20- Prof anderson

Assumptions of the classical Linear Model (Clm) e So far, we know that given the Gauss Markov assumptions, OLS IS BLUE e In order to do classical hypothesis testing we need to add another assumption(beyond the Gauss-Markov assumptions) Assume that u is independent of x,x2…,xk and u is normally distributed with zero mean and variance 0: u- Normal(0, 02) Economics 20- Prof anderson