Estimating the Risk of Death from Air Pollution

Assessment of Deaths Attributable to Air Pollution: Should We Use Risk Estimates based on Time Series or on Cohort Studies? ( 6 page pdf, N. Künzli, S. Medina, R. Kaiser, P. Quénel, F. Horak, Jr., and M. Studnicka, American Journal of Epidemiology, Vol. 153, No. 11, 2001)

Today’s review looks at an analysis of the two ways of estimating the risk of death from air pollution- as an event from immediate pre-death conditions over a short time (using time series) or as a cumulative result over a lifetime using cohort groups. The authors suggest that each risk estimate has value and each has strengths and weaknesses. The analysis could be useful in suggesting what and how often to monitor and how to use the data.



Key Quotes:

“The “frailty” concept is useful in acknowledging that, in most cases, the probability of death is influenced not by one single factor, e.g., air pollution, but rather by a function of a whole set of underlying conditions or risk factors”

“Time-series studies model the association between the probability of death and the level of air pollution shortly before the event”

“Cohort studies model the association between an exposure and time to death. Thus, in cohort studies, time is the outcome measure of interest.. the cohort study design requires a setting with spatial variability of long term exposure”

“several patterns of exposure may influence time to death:

1. a single exposure occurring once in the past over a short period of time (e.g., an accidental spill);
2. repeated exposures of short duration;
3. continuous exposure over a longer period of time;
4. a pattern of short term exposure just before death; or
5. a combination of all of the above”

“categories of death associated with air pollution:

• air pollution increases both the risk of underlying diseases leading to frailty and the short term risk of death among the frail;
• air pollution increases the risk of chronic diseases leading to frailty but is unrelated to timing of death;
• air pollution is unrelated to risk of chronic diseases but short term exposure increases mortality among persons who are frail; and
• neither underlying chronic disease nor the event of death is related to air pollution exposure”

“we have conceptually shown that time-series based numbers of attributable cases must underestimate the total effect”

“assuming the availability of long term air pollutant monitoring data, exposure may be defined for different periods of life and for a variety of patterns (e.g., number of peaks, seasonal averages, cumulative exposure, etc.)”

“both types of air pollution mortality studies— the time-series approach and the cohort approach—are of value in air pollution epidemiology. However, they measure two different aspects of mortality that are not interchangeable”

Related articles

• Air Pollution Preconditions for Heart Attacks (pollutionfree.wordpress.com)
• Air Pollution Exposure and the Health of Neighbourhoods in Ottawa, Canada (pollutionfree.wordpress.com)
• The State of Air Pollution in Europe (pollutionfree.wordpress.com)
• Reviewing the air pollution death and health impact numbers and peer reviewed epidemiological studies (nextbigfuture.com)