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Launching a Longitudinal Study

How do They Find and Track All Those People?

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Updated April 04, 2012

Launching a Longitudinal Study

The CLSA will collect up to 348 million pieces of data

Dana Hursey Photography / Getty Images

When health writers cite statistics, particularly in the area of aging, they’re often relying on data collected in long-term, longitudinal research. What may take only a moment to quote, however, can be the result of thousands of man-hours spent over many decades of painstaking, detailed information gathering and synthesis, sifting through mounds of questionnaires, testing samples, and scrutinizing trends. These are the projects that inform our understanding of how the body ages, the changes it undergoes over time, which behaviors hinder your longevity and which improve it.

To help you understand how such a massive undertaking gets planned and executed, here’s a look at one such large-scale study – the Canadian Longitudinal Study on Aging (CLSA) – as it’s getting underway. The CLSA aims to track 50,000 men and women between the ages of 45 and 85, for a period of 20 years.

First proposed in 2001, the CLSA was granted final approval in 2011. During the intervening decade, much was taking place behind the scenes to prepare for the dual-track study’s launch. Approval of study design and survey questions, construction of data collection sites, a centralized laboratory for sample analysis, call centers, and specialized software to protect the privacy of participants all had to be completed before the real investigation began.

Open access to results: Principal investigator Parminder Raina told me the breadth of research data gleaned from such a long-term study far outweighs the challenges of coordinating its many components.

“This information will belong to all Canadians,” says Raina, an epidemiologist from McMaster University. “It’s not the property of any one researcher or institution. It will be a resource for anyone who wants to study the data for decades to come, as long as their project is reasonable, and complies with the restrictions we’ve put in place to protect the privacy and confidentiality of the participants.”

Two branches of study: There are two populations that will be investigated, both within the age range of 45-85 years at base line, that is, at the beginning of the research. All participants will be recruited randomly through phone numbers or using provincial population data from across the country. The difference between the groups, or cohorts, lies in how information will be gathered.

The first group, called the “Tracking Cohort”, is made up of 20,000 men and women in a random sample of the population. The subjects will be interviewed extensively by telephone every three years during the study period. Questionnaires will focus on a wide variety of medical, social, lifestyle and economic topics.

The second group, or “Comprehensive Cohort”, is made up of 30,000 men and women who will be investigated much more closely, in person. Ten cities across Canada, from the western-most province of British Columbia to the east coast province of Newfoundland, have been established as data collection sites. Again, participants are randomly selected but in this case, they must live within a 25-50 kilometer (15-30 mile) radius of the data centers for ease of access. Home visits every three years will track their state of health, emotional and social wellbeing, lifestyle factors, and disease development. Lengthier sessions at the data collection sites will record vital statistics like blood pressure, weight, bone density, strength, and balance.

Halfway through each three-year period, all the participants will be contacted to update their files.

In all, an estimated 348 million pieces of data are expected to be collected. Making this longitudinal study unique is its paperless mandate – which poses an even greater challenge for systems designers and epidemiologists on the project. Lead investigator Raina says the extra work will pay off, in the long run.

“It’s technically easier to launch a paper-based study, with questionnaires and signatures – but it’s a nightmare for maintenance and checking data because everything has to be entered manually into the computer software, which can take years,” he notes. “Having data go immediately into the system means any mistakes are flagged right away, and we can analyze the data very quickly.”

Other countries have a long history of long studies – Britain, for example, has supported a few longitudinal birth cohort investigations, with a mandate to follow subjects from birth to death. Still, Raina says he’s thrilled to head Canada’s first large-scale study on aging.

“This project will definitely outlive me,” he says. “It will be collecting information for twenty years, and the results will be studied for another fifty or sixty years after that. There are people that have not even been born yet, who will be studying this data.”

More information on the Canadian Longitudinal Study on Aging

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