One survey revealed a threefold increase in breast cancer.

一项调查显示乳腺癌的发病率已是原来的三倍。

《柯林斯英汉双解大词典》

The graphs show a threefold increase in the number of…

该图表剖明…的数目增添了三倍。

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Meanwhile, the number of people over 65 will be rising to 300 million by 2050, a threefold increase.

与此同时，65岁以上的人的数目到2050年将上升到30亿，增长了三倍。

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Please understand, we do not see a threefold increase in the money supply via the private banking system, here and now.

FORBES: Monetary Watch June 2011, Inflation prospects post QE II

Bosch reckons that for electric cars to become universally popular, a threefold increase in energy density and a fall of two-thirds in the price of batteries will be needed.

ECONOMIST: The electrification of motoring

The spokesman said Mr. Schultz's pay is tied to company performance and that his gains reflected a more than threefold increase in Starbucks's share price since he returned as CEO in 2008.

WSJ: As Tax Hikes Loomed, Some CEOs Sold Company Stock