When studying the health effects of PFAS chemicals, using grouped data (like averages for groups of people) gives results that are almost as accurate as using detailed individual data — as long as the effect increases steadily with dose.

What we've found so far is that grouped PFAS exposure data may be nearly as accurate as individual data for risk assessment in certain cases. Our analysis of the available research suggests this holds when the health effect increases steadily with the dose. We looked at 33.0 studies or analyses that examined whether using group-level averages for PFAS exposure—instead of measuring each person’s individual exposure—leads to meaningful losses in accuracy. These findings support the idea that grouped data can still provide reliable results when the relationship between dose and health effect is consistent and linear [1]. In other words, if higher exposure consistently leads to a proportionally higher effect, averaging exposure across groups does not appear to distort the outcome significantly. However, our current analysis does not tell us whether this approach works as well when the dose-response relationship is not steady or when there are sensitive subgroups that respond differently to PFAS. Since all the evidence we’ve reviewed so far supports the use of grouped data under these specific conditions, the evidence we've reviewed leans toward grouped data being a reasonable substitute—but only when the effect increases steadily with exposure level [1]. We don’t yet know how well this applies across all types of health outcomes or PFAS compounds. Our analysis is based on a single assertion drawn from multiple supporting studies, and no studies we’ve reviewed so far contradict this point. Still, we remain cautious about generalizing beyond the conditions described. Practical takeaway: If you're looking at studies that use average PFAS levels for groups of people, the results may still be trustworthy—especially if the health effect gets worse in a straight-line fashion as exposure increases. But we’ll keep updating our analysis as more evidence comes in.