As it happens, most of the variation in the price of oil over the past 40 years has reflected changes in the value of the dollar (the denominator) rather than the value of oil (the numerator).

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Separate factories allow for more variation, but at the price of fewer economies of scale.

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The council document said following more detailed investigations a "variation" - or difference between the agreed price list, called the the "schedule of rates" - and the actual amount charged by MITIE was found.

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Three professors (from Stanford, INSEAD and MIT, respectively) have come up with a variation on this theme: that the price paid can also influence behaviour.

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Food director of British Retail Consortium, Andrew Opie said that there is "a variation in price between those in the top quarter of dairy production and those who aren't and farmers who are lucky are those in supermarket supply chains".

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And while they say there can be significant variations in some of these, it seems one of the reasons Brent crude continues to appeal is that there's least variation in its price, at around one US cent per barrel over a long period.

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The house-price measures compiled by the Halifax bank and the Nationwide building society are designed to avoid distortions caused by variation in the type of property being sold.

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