Further down, they explain the measurement errors involved:
"
If you buy the same product twice, how much will chemical levels vary?
When we bought two samples of the same product, plastic chemical levels differed on average by 59%, calculated as Relative Percent Difference (RPD).
To test whether completely identical samples would show different levels of chemicals, we sent about 10% of our products in triplicate. This means we sent three copies of the product from the same batch – with matching lot number and expiration date – bought at the same store on the same day. We found that the triplicate samples differed less – on average by 33%.
Our lab’s quality control methodology lists 20% RPD as an acceptable margin of measurement error for duplicate samples, meaning if you tested the exact same sample twice, you could see up to a 20% difference purely due to measurement noise. Taking that into account, the RPD for two samples of the same product (not necessarily from the same lot) ranges from 39-59%. For samples with the same lot number and expiration date, the RPD narrows to 13-33%.
Within-product variability appears high, possibly because we are dealing with very small chemical concentrations measured in nanograms."
Yep, I saw that section. To my interpretation, these average percents are so much smaller than the variation seen, that it's basically /not/ addressing the outlier variations.
Perhaps plots would be better/less alarming than easy-to-cherry-pick tables, but I'm not expert on conveying this sort of data either...
" If you buy the same product twice, how much will chemical levels vary?
When we bought two samples of the same product, plastic chemical levels differed on average by 59%, calculated as Relative Percent Difference (RPD).
To test whether completely identical samples would show different levels of chemicals, we sent about 10% of our products in triplicate. This means we sent three copies of the product from the same batch – with matching lot number and expiration date – bought at the same store on the same day. We found that the triplicate samples differed less – on average by 33%.
Our lab’s quality control methodology lists 20% RPD as an acceptable margin of measurement error for duplicate samples, meaning if you tested the exact same sample twice, you could see up to a 20% difference purely due to measurement noise. Taking that into account, the RPD for two samples of the same product (not necessarily from the same lot) ranges from 39-59%. For samples with the same lot number and expiration date, the RPD narrows to 13-33%.
Within-product variability appears high, possibly because we are dealing with very small chemical concentrations measured in nanograms."