La meilleur de tousles tarifs serait celui qui ferait payer a ceux qui passent sur une voie de communication un peage proportionnel a l'utilite qu'ils retirent du passage.1—Jules Dupuit, 1849.

Economists have paid very little attention to the statistical methods known as "factor analysis" or "component analysis." These methods were developed primarily by psychologists. Sociologists have also used them to some extent. These methods may eventually help economists to solve some of their...