WASHINGTON - Credit card brand Visa said Tuesday that, according to a national survey, the Tooth Fairy -- or parents acting discreetly in her name -- left an average of $3 (2.40 euros) under the pillow per tooth this year.

That’s up 15 percent from $2.60 a year ago, it said, making deciduous teeth one of the best investments out there.

“The tooth fairy may be the canary in the economic coal mine,” said Jason Alderman, Visa’s senior director of global financial education, echoing hopes that the US economy might yet snap out of its post-recession blues.

Visa is promoting a smartphone app to help parents figure out exactly how much a fallen tooth is worth, as part of a global program to better educate families about money.

Its Tooth Fairy findings were based on a telephone survey of 2,000 households across the United States in mid-July, with a margin of error of plus  or minus four percentage points.