[tdonovic]

All the tap water in Australia is fluoridated. You would be considered a bit odd if you drink filtered water instead of tap water (bar say SA where the water tastes bad). All other things equal, we should expect 3&4 yearolds to have a 3.66 higher IQ than those, say, in NSW, where the water is treated and tastes good enough to drink?

Surely there are some population effects or something else going on here, or the effect, especially later on in life, evens out between the groups.

[aplummer]

Particularly with the nationwide school test scoring, there should be statistically significant score differences in QLD (only recently fluoridated).

[ruytlm]

Could look at Warrnambool (VIC) as an example, as I believe they only started fluoridating in 2008.[0]

Likewise, I understand several council areas in Queensland stopped fluoridating in around 2016.[1]

[0]: https://hnb.dhs.vic.gov.au/web/pubaff/medrel.nsf/LinkView/08... [1]: https://www.abc.net.au/news/2016-09-28/mackay-council-vote-s...

[RustyRussell]

SA (really, Adelaide) is very region specific, though. I grew up drinking tap water here, though I've had some strange tasting water in other suburbs