[wolpoli]

> If you look at murder rates in the UK they peaked in the early 2000’s. Maybe those abused boys were taught violence is the answer?

There were earlier HN posts attributing the decline in the rate of murder rate/violence crime to countries phasing out lead-gasoline. Now we might never know unless we do a properly controlled experiment.

[talideon]

We've seen exactly the same pattern everywhere in the world when leaded petrol was banned. At this point, we've had our controls, because different countries scrapped lead at different times, and exactly the same trend has been observed. Think of the ones who scrapped it later as acting as the control group for those countries who scrapped it later.

Besides, the effect of lead on the human brain had been well known before leaded petrol was banned.

[thaumasiotes]

https://www.gla.ac.uk/media/Media_774797_smxx.pdf

> We perform the first meta-analysis of the effect of lead on crime by pooling 529 estimates from 24 studies. We find evidence of publication bias across a range of tests.

> When we restrict our analysis to only high-quality studies that address endogeneity the estimated mean effect size is close to zero.

> When we use the full sample, the mean effect size is a partial correlation coefficient of 0.11, over ten times larger than the high-quality sample.

Interestingly, I met someone on HN once who insisted that effect sizes are always smaller in larger trials because that's just the nature of reality. This does not say anything good about scientists' conceptual understanding of what they're doing.