Introductory econometrics: A modern approach. Wooldridge JM. JM Wooldridge - 2015 - books.google.com GSID: vI9x-W_gVY8J
Econometric analysis of cross section and panel data. Wooldridge JM. JM Wooldridge - 2010 - books.google.com GSID: T5fz2cmyyF8J