Here's how it works: Researchers give people working in pairs three sets of 12 questions written on index cards.

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Foreign journalists with video cameras are still working in central Iraq, but now circumstances are such that when they leave their fortified compounds, they must travel in pairs of cars, accompanied by armed guards.

ECONOMIST: Iraq documentaries

Another American scientist, Robert Plomin, has been working with 25, 000 pairs of identical and non-identical twins in Sweden.

ECONOMIST: WHAT WE LEARN FROM TWINS: The mirror of your soul | The

Mr Plomin has also set up a study working with 10, 000 pairs of identical and non-identical twins in Britain.

ECONOMIST: WHAT WE LEARN FROM TWINS

My son got two pairs of Skullcandy earphones in a row and each time they stopped working after a month.

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