As a result, he said all customers would be able to choose between two types of tariff - variable and fixed - and receive more transparent bills.

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When you look closely at how the two groups compare you see quite quickly that the extent of Internet-use was only one variable that differentiated the two groups being studied.

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Those two come-ons sell a lot of variable annuities.

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The proportion of workers on flexible hours has nearly doubled since 1991, to almost 30%, and two-thirds of all workers now earn some variable pay (bonus, profit share and so on).

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The Free Fighter includes four fully customizable macro buttons for quick access to combos, as well as two variable speed turbo buttons for fast, slow or user-created tap speed.

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Disentangling the two relationships is impossible unless a third variable with the right statistical properties, a so-called instrument, can be found and exploited.

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The company is also working on continuously variable darkening (current models have only two settings) and windows that are powered entirely by self-contained solar cells.

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Fixed-rate mortgages are due to expire for about two million people over the next 18 months, reverting to high variable rates.

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