I’ve only read the abstract as the full PDF seems to be paywalled, but the 15 points of gain seem to be limited to “the one quarter of the population most deficient in iodine”. The abstract says the estimated gain for the population as a whole was “roughly one decade’s worth of the upwardtrend [sic] in IQ in the US”, which is 3 points (from memory).
I’ve only read the abstract as the full PDF seems to be paywalled, but the 15 points of gain seem to be limited to “the one quarter of the population most deficient in iodine”. The abstract says the estimated gain for the population as a whole was “roughly one decade’s worth of the upwardtrend [sic] in IQ in the US”, which is 3 points (from memory).
Yes, thanks for pointing that out. I was aware of that but apparently phrased it really badly in my summary.