The lab number is just an estimate, it's subject to some normal variation and it naturally declines with age.

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Some variation is normal, but if it gets too long it can upset the timing of heartbeat with potentially dire consequences - dizziness, faints and, rarely, sudden death.

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The difference was equivalent to the average variation in cognitive scores between children born at a normal gestational weight and those weighing less than 3.5 pounds, the researchers said.

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It is encouraging that the characteristics of this group of cloned calves apparently fall within normal ranges, although in some cases the data is presented in a way that does not show variation.

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Normal sleepers, however, showed the highest food variety in their diets, and very short sleepers had the least variation in what they ate.

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