Another factor is volume of sales.

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Airships demonstrate a law of increasing returns: doubling the length increases the surface area (and hence weight) by a factor of four while the volume (and hence lifting capacity) goes up by a factor of eight.

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The Federal Highway Administration concluded that the main cause was a crack that grew undetected in one of the bridge's huge chain links, but that the high volume of traffic was also a factor.

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But Mr Oxley thinks the volume of new housing is only one factor affecting the real issue, which is affordability, or rather the lack of it.

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The scramble for stock opportunities and the consequent spike in trading volume has, increasingly, become a big enhancing factor in the bull market.

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Another significant factor is offshoring, which has reduced the volume of parts moved in and out and around the United States.

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Another factor that sparked margin expansion was higher payment volume.

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Some traders also pointed to declining volume, typical ahead of year-end, as a near-term factor likely to hold prices back.

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