In fairness, Maddison's time series which use MJ are pretty much the canonical source for the "look how much things have changed" graphs, and data errors make "

In fairness, Maddison's time series which use MJ are pretty much the canonical source for the "look how much things have changed" graphs, and data errors make "look, France was much richer than Poland" sort of comparisons" more dubious[1] But it's also not as relevant or surprising as it sounds, since the numerator of those fractions is also guesswork. They're not dividing accurate figures for the total wealth of European countries to get an inaccurate estimate of how rich the "average" person was, they're actually tending to work the opposite way from scant data on wages, prices and what "average" people owned multiplied by scant data on population to get a wealth of the nation figure[2]. Needless to say, there's a lot of margin for error subjectivity and scope for the introduction of personal biases in those estimates too (not to mention the inequalities and completely different access to stuff that makes adjusting for purchasing power and comparing the wealth of Inca subjects, the average medieval Englishman, the average modern Equatorial Guinean and the average modern Briton from a single GDP per capita PPP metric pretty dubious) Essentially no economic theory (as opposed to economic history) depends on the accuracy pre-Industrial Revolution time series for inspiration or validation, and if you double the values for the period before the exponential growth curve, you still get an exponential growth curve. [1]except to the extent that the figures were guesstimated based on the consensus of historians that country X is much richer than country Y [2] cf modern Nigeria, where we have reasonably accurate census data and an "oops, using our new method of calculating GDP, it seems to have doubled previous estimates"