Analyze each of the following reports, explaining the ways in which the method of difference has been applied in the investigations recounted. Discuss the strengths and weaknesses of the method of difference as it is used in each case.

Here is some reassuring news for those whose career plans are slightly behind schedule: It turns out that peaking too early may kill you. That’s the finding of Stuart J. H. McCann, a professor of psychology at the University College of Cape Breton in Nova Scotia. McCann’s research concerns what he calls the “precocity-longevity hypothesis.” McCann analyzed the lives of 1,672 U.S. governors who served between 1789 and 1978 and found that those who were elected at relatively tender ages generally died earlier than their less precocious counterparts. Even when he controlled for the year that the governors were born, or how long they served, and what state they governed, the pattern held. No matter how he sliced the data, or ran the regressions, or accounted for various statistical biases, the story remained the same: governors elected to office at younger ages tended to have shorter lives. And what holds for state executives seems also to hold for other young achievers. McCann also analyzed smaller but more diverse sets of accomplished people—including American and French presidents, Canadian and British prime ministers, Nobel Laureates, signers of the Declaration of Independence, Academy Award winners, and seven centuries of Roman Catholic pontiffs. Again he found that “those who climb to the loftiest peaks in the shortest time also die younger. For the eminent, and perhaps for all, an early rise may lead to an early fall.”
—Personality and Social Psychology Bulletin, February 2003