Joseph Kitchin, 1861-1932, was a British statistician and businessman. In his “Cycles and Trends in Economic Factors”, 1923, he carried out a study on business cycles, in Britain and in the United States, between 1890-1922. Kitchin was able to identify evidences of the existence of very short business cycle, the so-called Kitchin cycle. These cycles have a duration of approximately 40 months, and he explained them as a result of psychological reactions to capitalistic production, and time lags in information, which affect the firms’ decision making process on commercial affairs.  In other words, this cycle responded to the adjustment between supply and demand in terms of market necessity and firms response.

Joseph Clemént Juglar, 1819-1905, was, as his compatriot François Quesnay, a physician turned economist. In 1862 he published his masterpiece “Des crises commerciales et leur retour périodique en France, en Angleterre, et aux États-Unis” in which he analysed economic crises in France, England and the United States from a monetary perspective.  He explained that periods of inflation and expansion are concluded when the central banking system contracts money supply. Although he was not the first to analyse and explain crises from such a point of view, he provided new ideas and perspectives.

Juglar was able to identify economic cyclical trends that helped develop the business cycle theory. He identified a medium economic cycle of between 7 and 11 years of duration, the so-called Juglar cycle. In this cycle one can identify trends in the investment levels and in unemployment.

Eugen Slutsky, 1880-1948, was a Russian mathematician, statistician and economist. In economics he is best known for his formulation of the Slutsky’s equation. Slutsky found an equation that splits income and substitution effects based on Hicksian and Marshallian demand curves. He developed this equation on his “On the Theory of the Budget of the Consumer”, 1915.

Slutsky did not produce any other significant contribution to economics, but he did produce fruitful works regarding mathematical statistics and probability theory.  He took special interest in the concept of asymptotic convergence in probability.

Video – Income and substitution effects:

Ernst Louis Étienne Laspeyres, 1834-1913, was a German economist, statistician and Professor in various universities. His most notable contribution to economics was the development of the Laspeyres index, used for the formulation of weighted indexes, so that each product that are included in them, have their own weight according to their real importance in the production, consumption, etc. He wrote about it in his “Die Berechnung einer mittleren Warenpreissteigerung”, 1871.

Laspeyres also wrote quite an amount of papers in the fields of economic history, the history of economic thought and on economic issues concerning his time.

Video – Laspeyres index:

Jean Baptiste Say, 1767-1832, was a French economist and businessman, and considered as the French disciple of Adam Smith and one of the exponents of mercantilism and classical economics.

Say’s chief work “Traité d’économie politique”, 1803, gathered up many of the ideas of his French predecessors and Adam Smiths, systematizing this masterful treatise, which nevertheless includes many original contributions. Thanks to it he gained recognition in Europe and at the other side of the Atlantic.

However, Say’s most important contribution to Economics was his apparently simple formulation of the Say’s Law (1803) that states, “products are paid for with products”. Later, in 1808, Scottish economist James Mill (father of the renowned John Stuart Mill), rephrased it as “production of commodities creates […] a market for the commodities produced”, and J. M. Keynes would rephrase it (although whilst making a point against it) in his “General Theory”, 1936, as “supply creates its own demand”, which is the better known restatement.

Jean-Baptiste Say was in touch with many economists of his era and carried out moderate debates with them, he distinguished himself as a more policy-oriented economist rather than a model-builder like David Ricardo.