The science of large numbers  pg. 4

Margaret Hargreaves, Ph.D., professor of Internal Medicine at Meharry Medical College, is co-principal investigator of the Southern Community Cohort Study. With her at the Matthew Walker Comprehensive Health Center in Nashville are (from left) technical assistant Lawana McKissack and health educator/coordinator Tamara Currin.
Photo by Dean Dixon
Both studies track participants by name, address, social security number, and in Shanghai, by citizenship IDs. The researchers regularly monitor government registries in China and the U.S. that track disease and deaths reported by health officials. Participants are also contacted periodically to update their disease and exposure information.

Biological samples—urine, blood, cheek cells (for DNA)—are sent to Vanderbilt University Medical Center, where they are stored in freezers for future analysis.

“We get boxes from up to 30 different centers every day,” Blot says. “The blood is separated into 14 different tubes and stored in a freezer bank.”

Once the data and biological specimens have been collected, the real detective work begins.

“We will do that through a ‘case-control’ study,” he says. “… We will identify everybody, say 500 people… who (have) developed lung cancer, and get their blood specimens. Then we choose a control group of 500 or 1,000 people (without cancer) who are the same age, sex, race, etc., and pull their blood specimens.

“Then we look for differences between the cases versus the controls. Meanwhile, we have all this background information on everybody, their smoking history and other factors.

“If the cause of a disease in this lower income population proves to be genetic, we should be able to apply our findings to higher income and higher education populations,” Blot continues. “Even environmental associations seen in the study population may apply more broadly, but we will examine these closely before making any extrapolations to other segments of society.”

Typically, during the first five years of an epidemiological study, most of the effort is devoted to recruiting study participants and collecting survey data and biological samples. The value of the cohort study increases as it is followed over the years and cohort members begin to develop different diseases.

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