More or Less Monday, 14 May, 2007 BBC Radio 4, 1630 BST Listen to programme Click here to have your say

In a set of extraordinary experiments, Paul Slovic, a professor of psychology at Oregon University, and his colleagues, have tested people's compassionate instincts when the scale of the need increases.

They showed one group a picture of a starving girl with text describing her plight. Another group was shown a boy and a third was shown the boy and girl together. All were asked for donations.

The result was that donations were equal for the boy and the girl on their own, but actually fell once they were together. For groups of five or 10, donations fell precipitously.

Why does compassion struggle so much with numbers?

We spoke to Professor Slovic about his work and its implications, including for the difficulty of mustering a response to genocide.

Plus, why economics may be ready for a makeover, and the last in our series on why numbers are not necessarily for blokes only.

Presenter: Andrew Dilnot
Producer: Michael Blastland

BBC Radio 4's More or Less was broadcast on Monday, 14 May, 2007 at 1630 BST.

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