Is That a Big Number?

Impressive statistics are thrown at us every day - the cost of health care; the size of an earthquake; the distance to the nearest star; the number of giraffes in the world. We know all these numbers are important - some more than others - and it's vaguely unsettling when we don't really have a clear sense of how remarkable or how ordinary they are. How do we work out what these figures actually mean? Are they significant, should we be worried, or excited, or impressed? How big is big, how ...