In a widely published story last week, The Associated Press mapped those scores to neighborhoods in a computer analysis that found the risks from industrial air pollution disproportionately affect minorities and the poor.
The story has stirred both controversy and intrigue in communities across America.
In Grand Rapids, Mich., the mayor has asked his air pollution experts to learn more about the risk scores, which were created by the Environmental Protection Agency in the Risk Screening Environmental Indicators project.
"It caught me completely by surprise, which shouldn't be for a mayor," George Heartwell said of the AP report on the EPA health risk scores.
The mayor said he never had been told EPA calculated industrial air pollution health risk scores for every square kilometer of the United States even as his office worked to reduce local pollution.
Michigan's Kent County, where Grand Rapids is located, had 26 neighborhoods in the top 5 percent nationally for the highest health risks scores calculated in 2000.
"That's disturbing," Heartwell said. "We have one of the highest incidences of childhood asthma in this country right here in Kent County and certainly part of that is related to the air quality."
In other places, community and industry officials have criticized the publication of neighborhood-by-neighborhood risk scores, saying they caused unnecessary alarm. Some regulators have even misidentified the source of the data used by AP.
The scientists who created and managed the EPA project say AP's report used the government data properly and helped inform the public about a program that cost millions of dollars but hadn't gotten much attention.
"The AP's analysis of health risks posed by industrial pollution across the country is a substantial contribution to the public's understanding of where greater attention needs to be focused," said Kathy Burns, a health scientist who spent nearly a decade working for EPA's main contractor on the RSEI project.
EPA says the RSEI scores are a valuable tool for screening and comparing communities' pollution and identifying those that might need further attention for health problems, but they cannot be used to predict the actual chances that residents in a community will get sick from industrial air pollution.
"Determining actual risks is complicated and time consuming to perform, which is why RSEI was developed as a risk-screening and priority-setting tool, and it should not be used to make determinations of actual risk," EPA spokeswoman Eryn Witcher said Thursday.
AP obtained the scores for the entire country from EPA under a Freedom of Information Act request and then, working with agency scientists, mapped the scores from the square kilometer grids used by EPA to the Census neighborhoods used to count the population in 2000.
The mapped scores were then used to compare neighborhoods and to identify the 5 percent with the highest health-risk scores per resident.
Steven M. Hassur, a retired EPA scientist who was one of the principle developers of the RSEI, was consulted by AP during the analysis and after its release. He said AP's mapping of the scores was "creative and comprehensive" and appropriate.
"They have carefully checked their programming calculations and output and appear to have accurately reflected the risk-related, grid-cell scores generated by RSEI," Hassur said of AP.
AP reported last week that the risk scores aren't designed to predict residents' exact chance of getting sick. Instead, they take into account the amount and toxicity of each chemical factory's releases into the air, the path the pollutants traveled and the number, age and gender of the people exposed. The goal is to identify communities with higher health risks that might need further attention.
Citing recent talking points issued by the federal EPA, the Illinois Environmental Protection Agency issued a statement to local newspapers that claimed AP had relied on data from the Toxics Release Inventory, which is the list of all toxins that factories report releasing into the environment.
The Illinois EPA said the TRI "fails to provide communities with relevant information on risks that may be present."
While TRI is one piece of information used by EPA to create the scores, the Illinois agency omitted that AP actually used the RSEI scores that were designed specifically to provide health risk comparisons on industrial air pollution.
The state agency declined to change its statement, saying it simply wanted to assure neighborhoods with high risk scores that the federal data has limitations and that it has its own more detailed way of studying air pollution with monitors.
"We were concerned that this information might have caused undue concern about health risks among the people who live in those neighborhoods," Illinois EPA spokeswoman Maggie Carson said.
An expert in political and government rhetoric said the Illinois agency's statement was a disservice to the public, omitting key information that would allow readers to properly evaluate the credibility of AP's story.
"The Illinois statement does not fairly represent the EPA talking points, and importantly, it leaves out information that the public had a right to know," said Kathleen Jamieson, director of the Annenberg Public Policy Center at the University of Pennsylvania.
Some communities with the highest risk scores were in rural areas not ordinarily associated with pollution problems because AP's analysis used risk scores calculated per person.
For instance, Caribou County, Idaho, ranked 13th nationally in health risk in the AP analysis. A Monsanto plant released 5,748 pounds of the highly toxic metal chromium in 2000 in a county of just over 7,000, accounting for the high per capita risk score.
Trent Clark, a spokesman for the Monsanto plant, said the county wouldn't have been in the top rankings if the AP hadn't used per capita calculations.
Burns, the contract scientist who worked extensively on the EPA project, said per capita measures are the fairest way to make comparisons countrywide.
"To compare the risks from one area to the next and fairly look at all communities, including rural communities, it is very important to consider the risks per person, and not per square mile," she said.