i agree with Edgar Potter, there seems to be a mispelling.

here's an excerpt of the original text, that i think shows that in the context anedoctal evidence was the term intended.

"In conclusion, beginning in the 1970's we had mounting evidence of the physical benefits of physical activity and initially had antidotal evidence for the emotional benefits. In more recent years, an increasing body of evidence points to mental health benefits that promote an even more successful outcome for patients who participate in exercise as part of their rehabilitation."

and for the definition of "evidência anedótica":

"Evidência anedótica refere-se a uma evidência informal na forma de anedota, ou de "ouvir falar".
O termo é geralmente utilizado em contraste com evidência científica, especialmente na medicina baseada em evidências, que é uma evidência formal. A evidência anedótica frequentemente não é considerada científica pois raramente pode ser analisada segundo o método científico."

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Note added at 22 hrs (2008-11-11 15:10:24 GMT) Post-grading
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as per Marcos Antonio's comment above, the expression "anedoctal evidence" is commonly misused by (we) English speakers as "antidotal evidence" (you can find more than one example, even in court record transcriptions...)