the Cowles Commission approach[2] the vector autoregression approach[3] the LSE approach to econometrics - originated with Denis Sargan now associated with David Hendry (and his general-to-specific modeling). Also associated this approach is the work on integrated and cointegrated systems originating on the work of Engle and Granger and Johansen and Juselius (Juselius 1999) the use of calibration - Finn Kydland and Edward Prescott[4] the experimentalist or difference in differences approach - Joshua Angrist and Jörn-Steffen Pischke.[5]