From some time in the 1900s until the late 1970s, in the US, iirc. https://www.cbpp.org/research/poverty-and-inequality/a-guide-to-statistics-on-historical-tre

From some time in the 1900s until the late 1970s, in the US, iirc. https://www.cbpp.org/research/poverty-and-inequality/a-guide-to-statistics-on-historical-trends-in-income-inequality https://www.cbpp.org/research/poverty-and-inequality/a-guide... Significant wealth inequality gaps and the lack of wage growth, in relation to inflation, coincide. There's a lot of data on this subject, but getting specifics on how the data is collected is very difficult (given the data collection is often decades old).