into graphical models as "wiping out" incoming arrows. This operation has subsequently led to Pearl's "do"-calculus and to a mathematical theory of counterfactuals in econometric models. Pearl further speculates that the reason economists do not generally appreciate these revolutionary contributions of Haavelmo is because economists themselves have still not reached consensus of what an economic model stands for, as attested by profound disagreements among econometric textbooks. References External links List of publications including the Nobel Lecture on 7 December 1989 Econometrics and the Welfare State Model Discovery and Trygve Haavelmo’s Legacy by David F. Hendry and Søren Johansen.] Trygve Haavelmo Growth Model by Elmer G. Wiens Econometricians University of Oslo alumni Alumni of University College London Norwegian mathematicians Norwegian Nobel laureates Keynesians Nobel laureates in Economics People from Skedsmo 1911 births 1999 deaths Neo-Keynesian economists Fellows of the Econometric Society Presidents of the Econometric Society 20th-century Norwegian economists Nortraship people People educated at Oslo Cathedral School