Ms. DUFFY: The big unknown factor in this race is what kind of role Dean Barkley is going to play and who exactly he draws vote from.

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Multiple-expansion is always an unknown factor in predicting stock returns.

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Mike Hancock, the Lib Dem MP for Portsmouth South agreed that comparisons were unhelpful, but argued it was difficult to make decisions about shipbuilding contracts with the "unknown factor" of the referendum.

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Singer notes a number of possible explanations for why the other two groups might not have seen the behaviors initially reported, including compensation thanks to other genes, some unknown environmental factor, or variability in the knocked-out gene.

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And that's the really - I think that's the big factor, the unknown here, is when do American consumers begin taking energy efficiency seriously?

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"We've investigated a number of accidents where there were distractions, " she said, adding that it's unknown whether cell phone use was a factor in this crash.

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Because so much is still unknown at this point, the main risk factor is people traveling to areas where cases have already been identified.

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The medical examiner said a contributing factor in Lee's death was "cachexia of unknown origin, " or malnutrition.

CNN: STORY HIGHLIGHTS

The final factor that will determine how the speaker comes out of this remains the biggest unknown.

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