Even if jury selection remains a crapshoot, the process has come a long way since the days of Clarence Darrow, who counseled that Presbyterians are often "cold as the grave," Baptists even "more hopeless," while Irishmen are the opposite, "emotional, kindly and sympathetic"
In the current Psychology Today, the new science of jury selection gets a critical look in "Unnatural Selection," by Matthew Hutson--
Jury consulting has become a big business over the past three decades. Hundreds of firms now rake in several hundred million dollars a year. Many offer "scientific jury selection" services, deploying demographics, statistics, and social psychology to cull potential jurors and engineer the perfect panel of people. But as these gurus aim to extract sure verdicts from parties of unknowns, their grasp on the chemistry of human nature appears to require a working knowledge of alchemy . . .. Despite all the money and research poured into predicting and shaping jury decisions, to a large degree the state of the art remains just that: art.
The alchemists who practice the art, however, think it's more: they call it "applied psychology." About half of jury consultants are psychologists. The others are "hail from a variety of fields—business, law, marketing, communications, theater, statistics."
For anyone interested in jury selection, "Unnatural Selection" provides a good overview of how jury consultants work and what they're looking for in jurors.