Question: Which British economist was Erwin Rothbarth a research assistant for that changed the theory of economics?
Context: Lionel Charles Robbins, Baron Robbins, (22 November 1898 – 15 May 1984) was a British economist, and prominent member of the economics department at the London School of Economics.  He is known for his leadership at LSE, his proposed definition of economics, and for his instrumental efforts in shifting Anglo-Saxon economics from its Marshallian direction. The Workers and Punks University in Ljubljana, capital of Slovenia, is an educational project that since 1998 each year from November to May on a topic selected by the WPU board runs a series of lectures based on social theories critical towards neoliberalism, including World-systems theory, applying selected, but not all, Marxian concepts to understand Slovenia as peripheral country, such as the theoretical work of Antonio Negri, Andre Gunder Frank, with participation from notable international academics, including American geographer David Harvey from City University of New York and philosopher Peter Hudis from Oakton Community College, British economist Michael Roberts, economist Joachim Becker from Institute for International Economics and Development Department at the Vienna University of Economics, Dutch economist Angela Wigger from Radboud University Nijmegen. Erwin Rothbarth (16 December 1913 – 25 November 1944) was a German economist and statistician.  He worked as a research assistant for John Maynard Keynes and made important contributions to the measurement of GDP and the modelling of individual consumption. John Maynard Keynes, 1st Baron Keynes {'1': ", '2': ", '3': ", '4': "} ( ; 5 June 1883 – 21 April 1946), was a British economist whose ideas fundamentally changed the theory and practice of macroeconomics and the economic policies of governments.  He built on and greatly refined earlier work on the causes of business cycles, and is widely considered to be one of the most influential economists of the 20th century and the founder of modern macroeconomics.  His ideas are the basis for the school of thought known as Keynesian economics and its various offshoots. David Henderson (born 1927) is a British economist.  He was the chief economist at the Economics and Statistics Department at the OECD in 1984–1992.  Before that he worked as an academic economist in Britain, first at Oxford (Fellow of Lincoln College) and later at University College London (Professor of Economics, 1975–1983); as a British civil servant (first as an Economic Advisor in HM Treasury, and later as Chief Economist in the Ministry of Aviation); and as a staff member of the World Bank (1969–1975).  In 1985 he gave the BBC Reith Lectures, which were published in the book "Innocence and Design: The Influence of Economic Ideas on Policy" (Blackwell, 1986). John T. Dingle is a British biologist and rheumatologist.  He joined the staff of the Strangeways Research Laboratory in 1959 as a research assistant to then-director Honor Fell, and later himself served as director from 1979 to 1993, taking over the position after the death of Michael Abercrombie.  His presence at Strangeways helped to move its research direction toward the original research interests of its founder, Thomas Strangeways, who sought to understand the physiology of arthritis and other rheumatic diseases, after many years in which the laboratory specialized more narrowly in tissue culture and cell biology.  Dingle was the president of Hughes Hall from 1993 to 1998, and is an honorary fellow.  He was the founding chairman of the British Connective Tissue Society (now the British Society for Matrix Biology), serving from 1980 to 1987.  Among his notable trainees is University of California, San Francisco cell biologist Zena Werb, who was a postdoctoral fellow with Dingle and subsequently worked as a research assistant at Strangeways. David Canning is a British economist.  He is Richard Saltonstall Professor of Population Sciences and Professor of Economics and International Health at the Harvard School of Public Health.  He holds a Ph.D. in economics from Cambridge University and is deputy director of the Program on the Global Demography of Aging.  Before assuming his role at the Harvard School of Public Health, Canning held faculty positions at the London School of Economics, Cambridge University, Columbia University, and Queen's University Belfast, where he received his B.A. in economics and mathematics. Nicholas Barr FRSA is a British economist, currently serving as professor of public economics at the London School of Economics (LSE).  He received his Ph.D. in Economics as a Fulbright Scholar from the University of California, Berkeley and his MSc in Economics from LSE.  According to his LSE biography, he has worked for the World Bank, "from 1990 to 1992 working on the design of income transfers and health finance in Central and Eastern Europe and Russia, and in 1995-96 as a principal author of the World Bank's World Development Report 1996: From Plan to Market."  He also served as an advisor to the British, Chinese and South African governments. Frank Horace Hahn FBA (26 April 1925 – 29 January 2013) was a British economist whose work focused on general equilibrium theory, monetary theory, Keynesian economics and monetarism.  A famous problem of economic theory, the conditions under which money (which is intrinsically worthless) can have a positive value in a general equilibrium, is called "Hahn's problem" after him. Helen Makower (1 June 1910 in London – 17 May 1998 in Marlborough, Wiltshire) was a British economist.  Graduating from Newnham College, Cambridge (M.A. Oxon, inc. awarded 1938, and with a Ph.D. in Economics (London School of Economics and Political Science) 1937, she joined Jacob Marschak's Oxford Institute of Statistics before serving in Frederick Lindemann's S-Branch, Sir Winston Churchill's private economics and statistics service, during World War II.  After the war, she served briefly with the British Control Commission in Germany and later with the United Nations, before returning to academia and the London School of Economics, where she retired as a Reader in 1977.  Makower was at the forefront of the statistical turn in the British economics of the 1930s, and remained an influential figure after the war, acting as an important link between the mathematical economics developed at the Cowles Commission and British economics.
Answer: John Maynard Keynes