<P><a href="http://www.richardsonlawrie.co.uk/pages/econometrics_introduction_modern_stata_using.php" target="_blank" >http://www.richardsonlawrie.co.uk/pages/econometrics_introduction_modern_stata_using.php</A></P>
<P><a href="http://www.eco.utexas.edu/faculty/Hamermesh/JEP92.pdf" target="_blank" >http://www.eco.utexas.edu/faculty/Hamermesh/JEP92.pdf</A></P>

<P><a href="http://qed.econ.queensu.ca/pub/faculty/abbott/econ452/" target="_blank" >http://qed.econ.queensu.ca/pub/faculty/abbott/econ452/</A></P>