And that elevated rate of brain cancer is statistically significant, though the analysis had certain limitations and the pattern easily could be due to chance, said Penn’s Timothy R. Rebbeck.
“These figures suggest that there’s an elevated risk of brain cancers in the baseball players compared to the general population,” said Rebbeck, a professor of epidemiology at Penn’s Perelman School of Medicine. “You can’t rule out the possibility that it’s random bad luck.”
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.
Posted: July 16, 2013 at 07:56 AM | 48 comment(s)