Many Western countries, most notably the US, had a major decline in their crime rate in the 1990s. About 20 years earlier, the US had banned the use of lead in gasoline. Perhaps you wouldn’t think those two facts are related - but many researchers think this wasn’t a coincidence.

After getting distracted and doing a whole episode on lead and IQ a couple of weeks ago, Tom and Stuart get to the subject they intended to cover: the lead-crime hypothesis. How strong is the evidence that the presence of lead in a child’s early environment increases their propensity for crime when they grow up? And how strong is the evidence that lead removal (at least partly) caused the declining crime rate?

The Studies Show is brought to you by Works in Progress, the magazine full of new and underrated ideas for advancing science, technology, and humanity. They have a new issue out right now, which opens with a fascinating essay on the decline of drink-driving. Check it out at worksinprogress.co.

Show notes

* Numbers on the US crime rate over time

* Evidence from Finland on IQ and crime

* The first study (to our knowledge) on the lead-crime hypothesis, from 2007

* Rob Verbruggen’s 2021 Manhattan Institute report on lead and crime

* Jennifer Doleac’s 2021 Niskanen Center report on lead and crime

* Paper focusing on 1920s/30s America and the impact of lead on crime

* 2020 Swedish paper on moss lead levels and crime

* 2021 PNAS paper on lead and personality change

* 2022 meta-analysis on the lead-crime hypothesis

* 2023 systematic review on the same topic

Credits

The Studies Show is produced by Julian Mayers at Yada Yada Productions.