Asser notes that no government agencies systematically collect data, and reliance on faith healing is not a category listed on a death certificate.
Before federal medical privacy laws were tightened, he was able to talk to medical examiners about cases, but that has become more difficult.
Asser has tracked a handful of cases that have gotten media attention in the past decade, including deaths in Philadelphia, Massachusetts and California. But he still learns about many of the deaths only through concerned friends or family members who contact him or Swan.
And death is not the only troubling outcome when children avoid doctors because of their parents' religious beliefs.
Beth Young, a professor at the University of Central Florida, says her hip dysplasia, which could have been easily corrected when she was an infant, went unnoticed and untreated by her Christian Scientist parents. Young finally went to a doctor in her 20s to find out why it was such a struggle to walk and climb stairs.
She learned her hip joints were deteriorating - but that it was too late for a surgical fix.
"It's not going to get any better," Young said in an interview. "I think about that every day. If my parents knew how simple the treatment was, I don't think they would have ignored it. So I do feel cheated."
She added: "I can remember times when I would pray and pray and pray, and I would think that maybe I'm healed now, and then I would go check, and I'd go walk in front of a mirror or something, and then I would discover, no I'm not."
Lyons, the Boston lawyer, has drawn national attention for defending parents in faith healing cases.
He successfully represented David and Ginger Twitchell, Christian Science parents in Boston who were acquitted of manslaughter charges in the 1986 death of their 2-year-old son from a congenital defect that caused the bowel to twist and become obstructed.
The landmark case caused enough concern to persuade Massachusetts lawmakers to abolish the religious exemption, said Jetta Bernier, executive director of Massachusetts Citizens for Children.
But even when such exemptions are abolished or revised, prosecutions can be difficult so long as parents show they are sincere in their religious beliefs, legal experts say.
"The status quo is very difficult to upset," said Jesse Choper, the Earl Warren Professor of Public Law at the University of California, Berkeley.






