Mr Kruse and Mr Blasi looked at dozens of studies covering the past two decades.

ECONOMIST: Economics focus

"Silver is being used in the products in the most robust industries, " said Chris Blasi, president of Wilmington, Del.

WSJ: A Wager on Metal's Silver Lining

The company quickly shut the messages down before they reached all of the intended recipients, says spokesman Ritch Blasi.

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Blank, Joseph Blasi, Douglas Kruse, Karen Lynn-Dyson and William A. Niskanen.

ECONOMIST: What has work become?