One of the most difficult things for our writers and researchers to confirm are the exact words of a famous quote, especially when the quote is not made in public and the source of the quote is dead.

Such is the case with Francois Mitterrand, who as president of France is reported to have described the then British Prime Minister Margaret Thatcher as having "the eyes of Caligula and the mouth of Marilyn Monroe."

It's a delightful quote and one that was a subject of a correction on our pages this week. It followed a Saturday profile of an Alberta politician which instead said Mr. Mitterrand described Ms. Thatcher as having the eyes of Stalin and the mouth of Ms. Monroe.

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Readers were quick to say no, it was Roman Emperor Caligula's eyes and not Stalin's.

A check of references suggested our readers were right. The Caligula reference was first noted in 1985 in the San Francisco Chronicle and has been repeated scores of times.

Then one of our staff said he had seen a reference to the Stalin quote and he was right as well. Jacques Attali, Mr. Mitterrand's former aide, insisted that the reference was to Stalin. He said this eight years after the original reference with the publication of his diary, Verbatim, in 1993 about the years that he worked with Mr. Mitterrand. He states that the former president was misquoted.

So you see how challenging this is. Even after Mr. Attali's book was published, the Caligula reference still outweighs the Stalin references by about 10 to one.

Is it possible both are right that Mr. Mitterrand loved the description so much he played with it to give a different despot's eyes as a comparison?

The Margaret Thatcher Foundation includes a Sunday Times article which firstly describes the famous Caligula quote, but also includes Mr. Attali's version.

And so that is why the correction this week said "Mr. Mitterrand is reported to have said".... It is true that he is reported to have said Caligula, although he was also reported to have said Stalin's eyes.

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Craig Silverman, who writes on newspaper errors for the Poynter Institute and has written a book called Regret the Error, said that when he was in New York a few years ago, he met with the head fact checker at Esquire Magazine. "I asked him what writers tend to get wrong, and he said it was often quotes from historical or popular figures that trip people up. These are often mangled or misattributed, and it can be tough to nail them down."

Mr. Silverman noted that it is a challenge faced by many organizations. "Research into newspaper accuracy in the U.S. has found that misquotes (of all varieties) are the most common mistake."

This has been a tricky one, but we endeavour to get names, titles and quotes right. And if readers question us, we try again to correct the record and fix any mistakes.

But as with this one, they aren't all easy.

If you have a comment on this or any other matter please comment below or send me an email at publiceditor@globeandmail.com