More or Less: Behind the Stats

Last week's mass-shooting at a cinema in Colorado has - not suprisingly - intensified America's bitter and long-running argument with itself about gun control. The argument is political and highly partisan. But it is also practical: would tighter gun laws actually lead to fewer gun deaths? You might think it's obvious that they would. But it seems the evidence isn't quite that clear. Also: how have Olympians changed in the last century?