“There has been a strong move toward the use of risk assessment instruments in the criminal justice system in recent years,” said John Monahan, a psychologist at the University of Virginia Law School who has been studying models of prediction since the 1970s. “The science of risk assessment is much better now than it was 20 years ago.” The instruments have gained traction not only as a public-safety measure, Monahan said, but because they allow for more efficient allocation of resources: When prison budgets are stretched thin, it makes sense to try to focus more funds o...