Such observations yield a wealth of correlations, but it is much harder to pin down causation.

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But there are other costs as well that are harder to pin down.

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But rare events like those that effect Tysabri are harder to pin down.

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The longer-term underestimation is harder to pin down, but even more dangerous.

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But Mr Clegg is harder to pin down than that.

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What they are is a lot harder to pin down.

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The Logan brand is even harder to pin down.

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Other tactics are harder to pin down.

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The details are harder to pin down.

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But she also cuts the figure of an impulsive woman, difficult to please, harder still to pin down, and known, lately, to be off her rocker, understandably so, because of her son's death.

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