The Norwegian economist Trygve Haavelmo began his career as a student of Ragnar Frisch at University of Oslo. He went to the United States in 1939 as a Fulbright scholar, where he ended up staying until 1947. Haavelmo spent much of his sojourn at the Cowles Commission, before returning to Oslo. He remained a professor a the University of Oslo until his retirement.

It was during his stay in the United States that Haavelmo wrote his most
influential work -- a 1944 article introducing the "probability approach" to econometrics. The "probability" approach argued
that we should envision existing economic data series as being "a sample selected by
Nature", i.e. randomly derived from a "hypothetical" series of distribution
which governed reality but which was unobservable. Thus, Haavelmo argued, we can test the
validity of economic theories by couching the *theoretical *model in terms of statistical relationships which
can then be tested. The relationship between theory and the hypothetical underlying
"reality", argued Haavelmo, is akin to the relationship between the observed
data and that "reality". Therefore, if we can come close in relating theory with
observed data in some precisely defined statistical manner, then we are effectively saying
we have "reproduced" another "natural drawing" from the hypothetical
"reality" and thus our theoretical relationships are in a sense
"true".

Haavelmo also addressed the issues of identification problems in simultaneous equations econometric problems (Haavelmo, 1943, 1947). It was Haavelmo who differentiated the "structural" from the "reduced" form equation and discussed the relationship between the original parameters and the reduced-form estimates. It was Haavelmo that introduced the "determinant condition" for identifiability. This set the ground for the "Cowles approach" approach to econometrics and the methodological debates on empirical economics that raged during the 1940s.

Haavelmo contributed to other areas of economics. In business cycle theory,
Haavelmo argued in an 1940 paper that one need *not* obtain oscillations as
a solution to a dynamic model as one can obtain business cycles with a monotonic
dynamical system, provided there is an appropriate pattern of shocks *a la*
Slutsky. Haavelmo is also responsible for the famous Keynesian "balanced budget
multiplier theorem" (1945).

In the 1950s, Haavelmo moved in more theoretical directions. In 1954, he published a book on growth theory with "skill accumulation" that anticipates many of the themes of modern "endogenous growth" theories. His most bold effort was in attempting to set out a micro-founded theory of investment (1960). Haavelmo identified the main problems of reconciling a theory of capital with a theory of investment. Trygve Haavelmo won the Nobel memorial prize in 1989.

- "The Method of Supplementary Confluent Relations", 1938,
*Econometrica* - "The Inadequacy of Testing Dynamic Theory by Comparing the Theoretical Solutions
and Observed Cycles", 1940,
*Econometrica* - "Statistical Testing of Business Cycles", 1943,
*RES* - "The Statistical Implications of a System of Simultaneous Equations", 1943,
*Econometrica* - "The Probability Approach in Econometrics", 1944,
*Econometrica* - "Multiplier Effects of a Balanced Budget", 1945,
*Econometrica*("Supp. Notes", 1946) - "Family Expenditures and the Marginal Propensity to Consume", 1947,
*Econometrica* - "Methods of Measuring the Marginal Propensity to Consume", 1947,
*JASA* - "Statistical Analysis of the Demand for Food: Examples of Simultaneous Estimation of Structural
Equations", with M.A. Girshick, 1947,
*Econometrica* - "Family Expenditures and the Marginal Propensity to
Consume", 1947,
*Econometrica* - "Quantitative Research in Agricultural Economics: The Interdependence Between Agriculture and the National
Economy", 1947,
*J of Farm Econ* - "The Notion of Involuntary Economic
Decisions",1949,
*EJ* - "A Note on the Theory of Investment", 1950,
*RES* - "The Concepts of Modern Theories of Inflation", 1951,
*Eknomisk Tidssk* *A Study in the Theory of Economic Evolution*, 1954.- "The Role of the Econometrician in the Advancement of Economic Theory", 1958,
*Econometrica* *A Study in the Theory of Investment*, 1960.- "Business Cycles II: Mathematical Models", 1968,
*IESS* *Variation on a Theme by Gossen*, 1972 (Swedish)- "What Can Static Equilibrium models Tell Us?", 1974,
*Econ Inquiry* - "Econometrics and the Welfare State", 1990,
*Les Prix Nobel de 1989*

- HET Pages: Theory of Investment
- Autobiography of Haavelmo at Nobel site.
- Curriculum Vitae of Haavelmo at Nobel site
- Press release of Nobel award (1989).
- Haavelmo profile at University of Oslo
- Haavelmo entry at Britannica.com
- Haavelmo Page at Britannica Guide to the Nobel Prizes
- Haavelmo Page at Nobel Prize Internet Archive
- Haavelmo entry at Bartleby
- Haavelmo Page at Laura Forgette

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