long-term evolution of value-proportions between the composition of production capital and the yield of production capital. Empirical research First empirical tests In the 1870s, Marx certainly wanted to test his theory of economic crises and profit-making econometrically, but adequate macroeconomic statistical data and mathematical tools did not exist to do so. Such scientific resources began to exist only half a century later. In 1894, Friedrich Engels did mention the research of the émigré socialist Georg Christian Stiebeling, who compared profit, income, capital and output data in the U.S. census reports of 1870 and 1880, but Engels claimed that Stiebeling explained the results "in a completely false way" (Stiebeling's defence against Engels's criticism included two open letters submitted to the New Yorker Volkszeitung and Die Neue Zeit). Stiebeling's analysis represented "almost certainly the first systematic use of statistical sources in Marxian value theory." Although Eugen Varga and the young Charles Bettelheim; already studied the topic, and Josef Steindl began to tackle the problem in his 1952 book, the first major empirical analysis of long-term trends in profitability inspired by Marx was a 1957 study by Joseph Gillman. This study, reviewed by Ronald L. Meek and H. D. Dickinson, was extensively criticized by Shane Mage in 1963. Mage's work provided the first sophisticated disaggregate analysis of official national accounts data performed by a Marxist scholar. Study in the late 1970s and onward There have been a number of non-Marxist empirical studies of the long-term trends in business profitability. Particularly in the late 1970s and early 1980s, there were concerns among non-Marxist economists that the profit rate could be really falling. Various efforts have been conducted since the 1970s to empirically examine the TRPF. Studies supporting or arguing in favour of it include those by Michael Roberts, Themistoklis Kalogerakos, Marcelo Resende, Minqi Li, John Bradford, and Deenpankar Basu (2012). Studies critical or contradicting the TRPF include those by Òscar Jordà and Simcha Barkai. Other studies, such as those by Basu (2013), Elveren Thomas Weiß and Ivan Trofimov, report mixed results or argue that the answer is not yet certain due to conflicting findings and issues with appropriately measuring the TRPF. From time to time, the research units of banks and government departments produce studies of profitability in various sectors of industry. The National Statistics Office of Britain now releases company profitability statistics every quarter, showing increasing profits. In the UK, Ernst & Young