Their root causes are poorly understood, but medical researchers suspect environmental factors are important.
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After all, the triggering process is unfamiliar and poorly understood, which naturally leads to suspicion.
Last year a new bankruptcy law came into effect, but it is incomplete and poorly understood.
Not long ago, hedge funds were a small, poorly understood and exclusive segment of financial services.
The basic mechanisms at work have been known for decades but the so-called "micro-physics" are poorly understood.
Both books deal with the pervasive threat of an invisible, poorly understood contagion that has no known cure.
With an ageing European population, brain disorders, while becoming a more important feature of healthcare, remain poorly understood.
We now have a cost-effective way to apply our methods to other poorly understood species in the Antarctic.
One of the radar analysts, atmospheric scientist Paul Kucera, said the West African weather systems are poorly understood.
Why some tasks should belong to one side of the brain and some on the other is poorly understood.
Asteroids are so poorly understood at this point that scientists cannot predict their exact locations, including that of Braille.
The way testosterone acts to turn a fetus male is still poorly understood.
Rubbish may be universal, but it is little studied and poorly understood.
Its cause derived, directly, poorly understood (both then and now), from Genoa.
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These are facts about guns that are well-known to the social scientists who study gun injury but poorly understood by the general public.
Such historical nuances, between men and ideas, and powerful men and their equally impressive fathers, are critical but poorly understood by outside observers.
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Because the methodology for calculating subsidy costs is not transparent and poorly understood, true project costs and risks are likely to be underestimated .
As the brain grows older, it undergoes complex and poorly understood changes from the biochemical, to the molecular, structural and functional that lead it to shrink.
They also use requisitioned land as collateral for bank loans, adding to the potential woes of a banking system in which risk is poorly understood.
Those chains can fold up in billions of different ways, and the process by which they arrive at the correct one is still poorly understood.
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This created an environment where researchers talked about HDL levels as all-important, ignoring the fact that HDL was much more poorly understood than bad cholesterol.
At least half of the damage, however, occurs hours later, as the initial injury sets off a complex and poorly understood chemical cascade that disables surrounding cells.
But he said it was seen as something separate, rather than a core part of the unscheduled care system and its contribution was "poorly understood across the NHS".
Did any of them bother to ask how likely it was that the people who so poorly understood the problem would be able to find the remedy for it?
But their products were complicated enough to create risks that were poorly understood - either by the trader himself, or by the people who were supposed to be overseeing him.
The other signals, such as behavior, are poorly understood.
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"Complex colour patterns such as spots and stripes are common in nature but the way they are formed is poorly understood, " said Dr Kathy Schwinn of the New Zealand Institute for Plant and Food Research.
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For it is here that the signal is really chopped into Leonardo-like categories before it finally emerges, by processes as yet poorly understood, as what the possessor of the brain in question perceives as visual reality.
"The physics of flight at such small scales is relatively poorly understood which makes designing small flying systems very difficult, " he told BBC News, adding that biological systems provided "critical insights into designing our own artificial flyers".
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One of the most persistent claims by CF believers is that cold fusion has, in fact, been duplicated thousands of times and that the perceived problems with reliably reproducing the results is due to subtle and poorly understood aspects of the materials used.
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