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This is breath-taking — but it also begs more questions than it answers.

Nearly 20,000 analysts’ recommendations sitting on the IBES research database, owned by Thomson Financial, were somehow doctored between September 2002 and May 2004, according to an academic paper due to be delivered in January to the American Finance Association’s annual meeting in Chicago.

This took the form of selective removal of analysts’ names from some of their historical recommendations, the anonymous New Economist blog in London writes, adding: “These were not random; they were concentrated among the worst performing recommendations.” Morton at Lazyfinance seems to have stumbled across the academic paper last week.

In an extract to Rewriting History, Alexander P Ljungqvist (Stern School of Business, NYU), Christopher Malloy (London Business School) and Felicia Marston (University of Virginia) declare:

“Comparing two snapshots of the entire I/B/E/S analyst stock recommendations database, taken in 2002 and 2004 but each covering the same time period 1993-2002, we identify nearly twenty thousand changes of an unusual nature: the selective removal of analyst names from historic recommendations (”anonymizations”).

“This practice turns out to be pervasive and non-random: Bolder recommendations are more likely to be anonymized, as are recommendations from more senior analysts, Institutional Investor “all-stars,” and those who remain in the industry beyond 2002.

“Abnormal stock returns following subsequently anonymized buy recommendations are significantly lower (by up to 11.0% p.a.) than those following buy recommendations that remain untouched, suggesting that particularly embarrassing recommendations are most likely to be anonymized.

“Analysts whose track records appear brighter due to anonymizations experience more favorable career outcomes over the 2003-2005 period than their track records and abilities would otherwise warrant. “

But who ordered the doctoring and who carried it out? Who has retrospective access to Thomson’s database? Did some investment banks feature more often than others? Or can any analyst re-edit what they’ve previously published on IBES?

Do let us know.