Deep-Rooted Data

The Carolina Population Center is in it for the long haul. The 52-year-old institution leads data-driven studies that span decades, enriching population research across the world.

Image of an hourglass in front of a world map
July 17th, 2018

Three projects –the National Longitudinal Study of Adolescent to Adult Health (Add Health), China Health and Nutrition Survey (CHNS), and MEASURE Evaluation – encapsulate the Carolina Population Center’s emphasis on long-term data collection. A central research approach of the center, these projects highlight the importance of longevity, enabling investigators to see links between issues, data, and outcomes.

“The reason we’re doing that is we can look at what has changed over time and it also helps us look at causality,” says Nancy Dole, the center’s deputy director of research services. “If something happened here did that cause some outcome at a later point? There’s value in following these cohorts for a very long time to address life changes.”

For projects to stand the test of time, though, Dole says they need to evolve.

“There can be studies that end because there’s not a whole lot more that they can collect to answer primary research questions,” she says. “There have to be new research questions asked.”

Take, for example, Add Health. When data collection began in 1994 it was expected to be a five-year study analyzing how social and environmental factors shape adolescent health. Twenty-four years later it has continued to follow participants into adulthood.

“We’re hoping Add Health will become an aging study,” says Kathleen Mullan Harris, the current director and principal investigator of Add Health. “And it’ll be the only aging study that begins in early adolescence and should continue and tell us a lot about the aging process and what matters.”

Barry Popkin, principal investigator of CHNS, says one way to continue the expansion of such studies is to embrace emerging technologies.

CHNS examines how the social and economic development of Chinese society is affecting the health of its population. When the survey began in 1989, researchers used survey questions as the main tool for data collection but have since expanded to include collecting biological measures like blood to assess white blood cell count and cholesterol.

“We’re looking to new ways as science changes to keep adding new dimensions – which allows us to be innovative and continue to be a kind of survey that our colleagues and reviewers will think is so important,” Popkin says.

A different approach

Add Health and CHNS are considered longitudinal studies. The surveys study the same variables – in both cases measurements from individuals, communities, and policies – over a long time period. MEASURE Evaluation differs because while it has been in effect for over two decades, it is comprised of shorter, singular projects.

Since 1997, MEASURE Evaluation has worked with governments and health institutions in developing countries to collect data for shaping public health programs.

“We help countries collect data and we collect data ourselves. Countries need data to understand where their health problems are, where their resources are, and how to get them to match up,” says Jim Thomas, director of MEASURE Evaluation. “We collect data on how best to improve their systems.”

Although MEASURE Evaluation doesn’t follow the same cohort over time like Add Health and CHNS, Thomas says changes are just as visible when looking back on the years.

“One of the most rewarding things about working with MEASURE Evaluation is seeing the difference that we have made,” Thomas says. “We’ve been able to make a difference because we are big – this is a big project working in many countries – and we have been around for a long time. When you look back over the years the changes are dramatic […] It’s actually moving the needle on how the world goes about doing public health.”

Nancy Dole is deputy director of research services at the Carolina Population Center.

Kathleen Mullan Harris is director and principal investigator of Add Health, a James Haar Distinguished Professor of sociology, and adjunct professor of public policy.

Barry Popkin is principal investigator of the China Health and Nutrition Survey, a W.R. Kenan, Jr. Distinguished Professor of nutrition and adjunct professor of economics.

Jim Thomas is director of MEASURE Evaluation Project and associate professor in the Department of Epidemiology.

Peter Bearman is a Jonathan R. Cole Professor of social sciences at Columbia University and former deputy director of Add Health.

 Barbara Entwisle is a Kenan Distinguished Professor of sociology and early contributor to Add Health.

Penny Gordon-Larsen is a professor and associate chair for research in the Department of Nutrition within the Gillings School of Global Public Health.