Richard Lynn was a scientist who infamously tried to estimate the average IQ of every country. Typical of his results is this paper, which ranged from 60 (Malawi) to 108 (Singapore).
Lynn's national IQ estimates (source)
People obviously objected to this, and Lynn spent his life embroiled in controversy, with activists constantly trying to get him canceled/fired and his papers retracted/condemned. His opponents pointed out both his personal racist opinions/activities and his somewhat opportunistic methodology. Nobody does high-quality IQ tests on the entire population of Malawi; to get his numbers, Lynn would often find some IQ-ish test given to some unrepresentative sample of some group related to Malawians and try his best to extrapolate from there. How well this worked remains hotly debated; the latest volley is Aporia's Are Richard Lynn's National IQ Estimates Flawed? (they say no).
I've followed the technical/methodological debate for a while, but I think the strongest emotions here come from two deeper worries people have about the data:
https://www.astralcodexten.com/p/how-to-stop-worrying-and-learn-to
