The Heath brothers, authors of Made to Stick, write,
A good statistic is one that aids a decision or shapes an opinion. For a stat to do either of those, it must be dragged within the everyday. That's your job -- to do the dragging. In our world of billions and trillions, that can be a lot of manual labor. But it's worth it: A number people can grasp is a number that can make a difference.See what they mean below.
Link: http://www.fastcompany.com/magazine/138/made-to-stick-the-gripping-statistic.html