A group at EPA has released a new FAQ on probabilistic risk assessment (PRA) that supports the thesis I’ve long held:

Range of probable risk = Science

Point estimates of risk = Politics

From the paper:

The use of point estimates in decision making might convey an unfounded high degree of precision. A probabilistic approach can be applied rather than defining a single value and might be less likely to imply undue precision. The display of results as a distribution can convey that no particular value carries specific risks of adverse effects; it also can support the understanding of the magnitude and likelihood of risk of adverse impact for a range of exposures, not just an individual point estimate of dose or exposure.

Decisions about risk management - what controls to put on activities in manufacturing, the workplace, environmental discharges, product use and disposal - are political decisions based on myriad social values of what's "safe enough" for whom and at what cost and should be informed by the best science on what the range of probable risks might be.  Then the regulator picks a number for compliance purposes.  Those who demand or communicate single point values of risk are misleading if they claim to be dictated by science.

You can also see the policy statement I worked on at the American Chemical Society for more background here.

Leave a reply