Psychology: Are there too many bipolar diagnoses among teens?

Not long ago I was talking to an older teenager who informed me that he had been diagnosed with bipolar disorder. He spoke of his moodiness, his quickly changing demeanor and his temper outbursts, most of which had begun around the onset of puberty. He had initially sought treatment after he had a "meltdown" following a breakup with his girlfriend. He said that, after reading about it, he was unsure if he really had bipolar disorder, and he laughingly spoke of how not one, not two, but three of his childhood friends had been diagnosed with the same problem.

What were the odds that four neighborhood friends from different...