I don't know if this info is on the web, because I heard it in the 70s or 80s, and since it was from historical research done by a "Marx Scholar" who marched to a different tune than the other 99.9% of his peers, it was likely quickly buried in Academia Lala Land ---
When Marx was publishing Das Kapital between 1867 and the early 80s, his central thesis was that industrialization was progressively making the plight of the lower classes worse & worse, decade by decade, as the factory owners got richer & richer.
His book was full of stats & tables & graphs, meticulously researched and presented to back up his thesis.
He obtained nearly all of his stats from the library of the British National Museum, the world's premier repository of the government and university and other types of publications having this kind of info. He hung out there daily for decades. The desk he used so often that it became "Marx's desk" has long since become a holy shrine to the Left.
The data showed a steady, unbroken decline from each decade to the next, ending at "this previous decade" - whichever that was (1840s? 1850s? 1860s? I forget).
And therein lies the rub. Because Marx did *not* include the 10 (or so) years prior to the publication of his book. He noted that the very latest stats were still being compiled and collected, and had yet to be published.
And I guess that sounded like a reasonable excuse to readers, given that all the local villages had to report their facts & figures to the townships, who had to collect & compile and then report the aggregated stats to the boroughs, who had to do the same and then report to the counties, who reported to the next level (regional govt centers? London?), and so on. And with everything done by hand with pen & paper back then, who knows how long this might take to finally appear in print at the British Natl Museum's Reading Room?
But this scholar was unwilling to accept Marx's reasonable sounding explanation at face value.
And his research turned up some very important facts:
CAVEAT: Sorry, but I'm only 2/3rds sure that "Das Kapital" was the book this Marx scholar was talking about. Perhaps I remember wrong, and it was actually his "Communist Manifesto" (1848) that ignored the stats from the most recent decade before publishing.
And Leftist have been following his example ever since.
If the facts dont support your argument ignore them or find a study that ignored them that you can quote.
Kind of similar to global warming "scholars" today who ignore climate data counter to their cause. Or, mainstream media "journalists" today who only report stories that support their agenda. Marx was a cunning liar, too.