Several definitions of econometrics exist, a popular example being the following: “Econometrics is the study of the application of statistical methods to the analysis of economic phenomena.” The variety of definitions is due to econometricians wearing many different hats. First and foremost, they are economists, capable of using economic theory to improve their empirical analyses of the problems they address. At times they are mathematicians, formulating economic theory in ways that make it appropriate for statistical testing. At times they are accountants, concerned with the problem of finding and collecting economic data and relating theoretical economic variables to observable ones. At times they are applied statisticians, spending hours with the computer trying to estimate economic relationships or predict economic events. And at times they ...