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Plausible upper bounds: are their sums plausible?
1United States Environmental Protection Agency, National Center for Environmental Assessment, Washington, D.C. 20460, USA.
Summary
Summing upper bounds for multiple cancer risks can be improbable but not misleading. Adjusting these sums downward can provide a more plausible estimate of overall cancer risk.
Area of Science:
- Environmental Health
- Toxicology
- Risk Assessment
Background:
- Quantitative cancer risk assessments often use upper bounds, not central estimates.
- Summing upper bounds is common for estimating combined cancer risk from multiple agents.
Purpose of the Study:
- To evaluate the plausibility and accuracy of summed upper bounds for estimating overall cancer risk.
- To determine if summed upper bounds provide misleading estimates of combined carcinogenic risk.
Main Methods:
- Analysis of four case studies involving multiple carcinogen risk assessments.
- Examining the relationship between the number of risk estimates and the probability/misleading nature of their sum.
Main Results:
- The sum of upper bounds becomes increasingly improbable as the number of risk estimates rises.
- Despite increasing improbability, the sum of upper bounds does not appear to be misleading.
- Overall risk is influenced by independence, additivity, number of estimates, and risk distribution shapes.
Conclusions:
- Sums of upper bounds offer valuable insights into overall cancer risk.
- Adjusting summed upper bounds downward can yield more plausible upper bounds or central risk estimates.