Generation What?

"But the practice of defining generations is more complicated than the theory. Often their labels are about as helpful as parents who imagine that if two children are 7, they should play together.
"Generations have a natural fluidity—it can be hard to say where one group ends and the next begins. And in the case of the current presidential campaign, some clashes between age groups are as contrived as the groups themselves."

Jenny Lyn Bader in The New York Times tries to figure out in which generations John McCain, Hillary Clinton, and Barack Obama belong.