You started your econometrics course by studying the OLS estimator extensively, first for the simple regression case and then for extensions of it. You have now learned about the instrumental variable estimator.
Question 2
To study the determinants of growth between the countries of the world, researchers have used panels of countries and observations spanning over long periods of time (e.g. 1965-1975, 1975-1985, 1985-1990).