In: Economics
Consider the instrumental variable regression model Yi = ?0 + ?1Xi + ?2Wi + ui where Xi is correlated with ui and Zi is an instrument.
Suppose that the first three assumptions in Key Concept 12.4 are satisfied. Which IV assumption is not satisfied when:
(a) Zi is independent of (Yi , Xi , Wi)?
(b) Zi = Wi?
(c) Wi = 1 for all i?
(d) Zi = Xi?