Finally, Meadow assumed that SIDS cases within families were statistically independent.

Typically in SIDS cases, a previously healthy baby is found dead in bed.

Emphasizing that most SIDS cases are unavoidable tragedies, Ms. Talan said, "We don't want the witch hunt days to come back," where grieving parents were considered suspects.

The doctor says that 80 percent of SIDS cases happen between two and four months, and that the advisories can make a real dent in the 6,000 cases a year.

By studying SIDS cases in Louisiana, Dr. Painter found that exposure to smoking after birth and never having been breast-fed were important additional risk factors.

"It seems like just a debate within the medical community right now" about what is a suspicious SIDS case, Mr. Borghesani said.

But the authors said that doctors at Massachusetts General did not report any suspicious SIDS cases between 1972 and 1995, even though 56 have now been tentatively identified by Dr. Truman's research.

Given a 5% male excess birth rate, there appears to be 3.15 male SIDS cases per 2 female, for a male fraction of 0.61.

During his investigations into other SIDS cases for his article, he finds that a copy of the book was at the scene of each death.

"Dr. Southall says in our piece that some studies suggest anywhere from 5 to 20 percent of SIDS cases may be murder," Ms. McFadden said.