The team did not respond to requests for comment.
Brain cancer can be caused by radiation and by certain rare genetic mutations, but the evidence for most other potential causes is unclear.
Studies suggest that estrogen and related hormones can protect against the development of brain cancer in women, said Geoffrey C. Kabat, senior epidemiologist at Albert Einstein College of Medicine in New York.
So it would be reasonable to examine whether anabolic steroids, which are related to those hormones, could play some role in brain cancer, Rebbeck said.
Occupational scientists also have looked to see whether any health issues are associated with synthetic turf, as some older kinds contained small amounts of contaminants such as lead, but there is no known link between the artificial surfaces and brain cancer.
The Inquirer identified 533 men who played for the Phillies between 1971 and 2003, and tallied the number of years they have been alive since then. For those who had died, the dates of death were taken from baseball-almanac.com.
Comparing cancer rates
The analysis then compared the rate of Phillies' brain cancers over that period with the rate of similar cancers in the adult male population, using data from the U.S. Census Bureau and a 2011 study in the Journal of the National Cancer Institute.
The national rate was 9.8 cases per 100,000 adult males per year, while the rate in the former Phillies was 30.1 cases per 100,000 - about 3.1 times as high. The national count included various kinds of glioma, such as glioblastoma - the aggressive form of cancer that struck all four former Phillies.
With Rebbeck's assistance, The Inquirer then calculated that this 3.1 figure had a 95 percent confidence interval of 2.1 to 4.1 - meaning that the elevated rate appeared to be statistically significant.
In lay terms, that means if one were somehow able to replay that 33-year period 100 times, you would expect the players' brain cancer rate to be 2.1 to 4.1 times higher than that in the adult male population 95 times out of 100.
But Rebbeck cautioned that the analysis required making certain assumptions that could substantially change the outcome.
For example, the population of Phillies from 1971 to 2003 was not adjusted for age. The rate of brain cancer varies with age, so when comparing populations, it is important that they have the same distribution of people in various age groups. The Phillies in the analysis range in age from their 30s to their 70s whereas the national population number includes men above and below that.
Furthermore, the nationwide brain cancer number for the 33-year period was based on cases counted in 2004 to 2007. A better approach would be to use the exact number of adult male brain cancers for each year from 1971 to 2003, as the cancer rate has declined slightly over time.
Attorney Brett A. Datto, a longtime friend of Daulton's, said the catcher and his family welcomed the analysis but felt it was premature to comment on any possible connection between cancer and baseball.
"Until we know more information about what may be a cause, if anything, then we're not in a position to comment," Datto said.
Two other teams - the New York Yankees and the Kansas City Royals - each have had at least three former players with brain cancer in the same era. As with the Phillies, the numbers are small enough that it could be bad luck.
To add another wrinkle, a sportswriter who covered the Phillies also died of brain cancer. Mike Ferretti, the Phillies beat writer for the Bucks County Courier Times in the 1980s and early 1990s, died of glioma in September 1993.
Jane Ferretti, Mike's mother, said she immediately thought of her son's case upon hearing about Daulton, and wondered whether there might be some connection.
"There's no answer sometimes," Ferretti said.
Vukovich played for the Phillies from 1970 to 1971 and from 1976 to 1981, and he was a team coach from 1988 to 2004. He died in 2007 at age 59.
McGraw, best known for striking out the last batter to seal the team's championship in 1980, pitched for the team from 1975 to 1984. He died in 2004, also at age 59.
Johnny Oates played for the Phillies just two years, in 1975 and 1976, spending most of his career on other teams. He died of brain cancer the same year as McGraw, at age 58.
Still another former Phillie, pitcher Ken Brett, reportedly died of brain cancer. But family members did not immediately respond to a query about the type of tumor, so he was left out of the Inquirer analysis.
Brett pitched here for just one year, 1973. One could argue that he - along with Oates, a Phillie for less than two seasons - should not be part of the Phillies' cancer toll because they played for the team for brief periods. If you took them out of the equation, that would lower the team's brain cancer rate.
But then you also would have to remove all the short-duration players who did not get brain cancer. Of the 533 Phillies, 187 played for one season or less. If you removed them from the analysis, the team's brain cancer rate would be higher.
Contact Tom Avril at 215-854-2430 or firstname.lastname@example.org.