During those years at Leiden, he had numerous discussions with Ehrenfest, Kamerlingh Onnes, Hendrik Lorentz, Pieter Zeeman, and Albert Einstein.

[6][7] After graduating, Tinbergen fulfilled his community service in the administration of a prison in Rotterdam and at the Central Bureau of Statistics (CBS) in The Hague.

[8] This topic was suggested by Ehrenfest and allowed Tinbergen to combine his interests in mathematics, physics, economics and politics.

[6][7] From 1929 to 1945 he worked for the Dutch statistical office and served as consultant at the Economic and Financial Organization of the League of Nations (1936–1938).

In parallel, he provided consulting services to international organizations and governments of various developing countries, such as United Arab Republic, Turkey, Venezuela, Surinam, Indonesia and Pakistan.

[16] It is generally believed to be the principle that, if the ratio between the greatest and least income exceeds 5, it becomes disadvantageous for the societal unit involved.

[17] Apart from specifics about a five-to-one ratio, it is true in general that Tinbergen's grand theme was income distribution and the search for an optimal social order.

[20] Tinbergen's classification remains influential today, underlying the theory of monetary policy used by central banks.

[21] Tinbergen's work on macroeconomic models was later continued by Lawrence Klein, contributing to another Nobel Memorial Prize in Economic Sciences.