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Making sense of the numbers: Air Health Trend Indicator

Daily exposure to air pollution can affect our health, potentially leading to chronic lung disease, heart attacks, strokes, and even death. Health Canada Research Scientist Dr. Hwashin H. Shin uses her expertise in mathematics and statistics to better understand the link between air quality and the health of Canadians.

As a statistician, Dr. Shin turns multiple sets of data into meaningful information, using statistical models to detect trends and show how Canadians have been affected by the air they breathe. This requires the sorting and interpretation of enormous amounts of data from all over Canada, gathered over a long period.

The Air Health Trend Indicator (AHTI) was developed to monitor the public health impact of air pollution in Canada, in order to support the long-term goal of clean, healthy, and sustainable communities for all Canadians. Through her research and statistical modeling, Dr. Shin is able to translate the data reported by the provinces and territories into knowledge to help guide policy for better health.

“The AHTI is an ongoing initiative as part of the Canadian Environmental Sustainability Indicators (CESI) program,” explains Dr. Shin. “We are examining the impact of short-term exposure to ambient air pollution on Canadians, in particular ground-level ozone (a colourless and highly irritating gas that forms just above the earth’s surface) and fine particulate matter known as PM2.5.”

Making sense of the numbers is a complex task. The AHTI measures the proportion of deaths that can be attributed to short-term exposure (for example, within a 2-week period) to ozone and PM2.5, tracking data across 24 Canadian cities. When we repeat this measure each year covering a long period of time, such as 20 or 30 years, we begin to see some trends and determine if they are increasing, decreasing or stable.

For example, to reflect the reality of our daily exposure, Dr. Shin has developed a new approach to estimate the adverse health effects of the two pollutants simultaneously. “Our new method allows two pollutants to be incorporated into a single statistical model to avoid overly attributing risk to a specific pollutant,” says Dr. Shin. “This provides a more advanced model which may be more appropriate to estimate combined health risks to Canadians from the two air pollutants simultaneously.”

Another factor that can complicate the interpretation of the information is the fact that some subpopulations may be more vulnerable to variations in outdoor air quality. For example, Dr. Shin’s research was recently recognized for its efforts to distinguish health impacts of air pollution based on gender. Dr. Shin was able to show that women and men were at different risks of mortality and hospitalization, which needs further investigations using more data. This analysis ensures that care is taken to identify any differences in health risks so all Canadians can be better protected.


Let’s draw attention to the incredible work of women in science! This article is part of a month-long series celebrating women in science, from International Day of Women and Girls in Science (February 11) to International Women’s Day (March 8).


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