“Leprechaun Hunting & Citogenesis”, 2014-06-30 (; backlinks; similar):
Many claims, about history in particular, turn out to be false when traced back to their origins, and form kinds of academic urban legends. These “leprechauns” are particularly pernicious because they are often widely-repeated due to their growing apparent trustworthiness, yet difficult to research & debunk due to the difficulty of following deeply-nested chains of citations through ever more obscure sources. This page lists instances I have run into.
A major source of leprechaun transmission is the frequency with which researchers do not read the papers they cite: because they do not read them, they repeat misstatements or add their own errors, further transforming the leprechaun and adding another link in the chain to anyone seeking the original source. This can be quantified by checking statements against the original paper, and examining the spread of typos in citations: someone reading the original will fix a typo in the usual citation, or is unlikely to make the same typo, and so will not repeat it. Both methods indicate high rates of non-reading, explaining how leprechauns can propagate so easily.