Where you live plays an important role in determining your health. Six-digit postal codes are often used in health research to identify where people live and to work out environmental exposure measures, which are then linked to health data.
Over the next several years Canada Post will transition five million Canadians to community mailboxes. Initially, eleven communities will test this transition, including neighbourhoods in Calgary, Winnipeg, and Halifax. With this change, postal codes will be assigned to community mailbox areas instead of smaller postal code areas.
Currently, postal code areas are around the size of a city block, while the new community mailbox areas will be considerable larger and less uniform in size. This change has important implications for health research.
Assigning people to a geographic location based on their community mailbox location will increase what is called ‘positional error.’ This positional error is based on the difference between an assigned location and someone’s actual location. Using a single community mailbox to represent multiple postal codes will reduce the precision of health research because researchers often take an average income of a postal code to represent the socio-economic status of an area.
"The changes planned at Canada Post have important implications for the health of all Canadians."
Using the average of a postal code may seem like a bad idea but studies have shown that these averages are a reasonable estimate of individual income for small areas. Community mailboxes will mean that the areas used for averaging income will get bigger and will be less like the average person in the area. Does the community mailbox that Tom, Pete, Deb, the students, and I share represent us? How well does it represent us? What about my mother in law, who gets her mail in a small town but lives at a lake?
In addition, Statistics Canada has found that postal codes assigned to community mailboxes increase linkage errors between health data and census neighbourhood. Meaning it’s harder to match your health data to where you live. Think of my mother in law. She lives 10Km from her postal code but we often use her postal code to match with her health data and average health data about the area.
Community mailboxes are already in place across Canada, particularly small towns and rural areas. They tell us an important story about our health. We can look to the research comparing linkage and positional errors in urban and rural areas to get a sense of what the change will mean for the rest of Canada. It’s been shown that survival inequalities in small towns and rural areas are lower than elsewhere when an area-based measure of socioeconomic status is used.
In another study it was found that in rural areas the mean distance error for access to the closest hospital is 3285 meters compared to a mean of 414 meters in urban areas. Would you be willing to accept that research and government policies be based errors of over 3Km between your home and the hospital?
The changes planned at Canada Post have important implications for the health of all Canadians and should be addressed by the research community, Statistics Canada, and Canada Post. The eleven pilot communities can serve as an important case study to evaluate potential measurement error and biases in health research, work which could accompany the transition to community mailboxes.
Dr. Daniel Fuller is the Canada Research Chair in Population Physical Activity at Memorial University, and previously an Assistant Professor in the School of Public Health at the University of Saskatchewan. He received his PhD in public health from the University of Montreal with a specialization in health promotion. Dr. Fuller’s research interests include population health, social inequalities, physical activity, the built environment, and natural experiments. Find more information here.
Dr. Martine Shareck is a post-doctoral research fellow at the London School of Hygiene and Tropical Medicine. She earned her PhD in Public Health at the Université de Montréal School of Public Health. Find more information here.