It seems noteworthy, but not commented that I can see (in the article), that the different samples of "Boba Guys Black Tea Pearls" have 20x variation in measured amount.
So what's up with that? (I have uninformed ideas...)
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."