After Darren Daulton died of brain cancer on Sunday, fans were reminded once again that the same malady had struck former Phillies Tug McGraw, John Vukovich, and Johnny Oates.

All four played for the team during the Veterans Stadium era. Coincidence?

In 2013, when Daulton first announced his illness, the Inquirer analyzed the numbers for all 533 men who played for the Phillies between 1971 and 2003. The result: the rate of brain cancers in that group was roughly triple the rate of the deadly disease for the overall adult male population.

But that could very easily have been due to chance, experts said at the time.

Epidemiologist Timothy R. Rebbeck, then at the University of Pennsylvania and now at Harvard University, stands by that statement. While it is theoretically possible that the four players shared some common exposure that increased their risk of brain cancer, Rebbeck said it would be difficult to pinpoint.

Fans have asked if something in the stadium, such as the artificial turf, was to blame, but there is no evidence that is the case. Others have wondered if steroids could have played a role, though there is no proof that was the culprit, either. Daulton, who died of a type of brain cancer called glioblastoma, did not go into specifics but acknowledged using drugs while playing. The others played well before the steroid era.

"You wouldn't necessarily want to rule out that there is something else going on here," Rebbeck said Monday. "But it would be hard to hypothesize what that might be."

With dozens of professional sports teams, it is not unreasonable to expect that at least one of them would have a higher-than-average rate of some type of cancer, said Rebbeck, who is a professor of cancer epidemiology at Harvard's Chan School of Public Health and a professor of medical oncology at the Dana Farber Cancer Institute.

"Just by random chance, you will get some clusters that pop up," Rebbeck said. "What's almost always been the case is that it's nearly impossible to explain those clusters."

Rebbeck cautioned that the Inquirer analysis of the Phillies' brain cancer rate had limitations.

Chief among them: the number was not adjusted by age.

The Phillies in the analysis ranged in age from their 30s to their 70s, whereas the population for the national brain cancer rate included men older and younger than that.

What's more, the national rate was based on cases counted from 2004 to 2007. A better approach would be to use the number of adult male brain cancers in each year from 1971 to 2003, as the rate declined slightly during that period.