Decreased Crime

It's not the water quality, it was a no-knock agent to help improve the shelf life of engines and make them run smoother. You know when an old engine starts to make a chuk chuk chuk noise? That's combustion occurring at the wrong part (anywhere but the centre) of the cylinder. Before improvements in refining petrol and building engines were made, the only solution to this was to add something to it. Several things were tried and could replicate the effect, but tetraethyllead was chosen because it didn't smell and didn't give off a funny colour.
Wrote this out and realised you were talking about the present day, posting just because it may interest someone who can't be bothered looking it up themselves.

* Large increase in police population
* Longer jail sentences, not as a deterrent but just that people in jail can't commit crimes
* Decrease in lead levels in the air as a result of environmental regulations and capital flight
* Legalized abortion means less kids in poverty
* Gun control regulation, not assault weapons bans but background checks and wait periods reduce crimes of passion

At least that's the case in the U.S. Doesn't really attack the root of the problem, which is poverty and inequality. Say what you want about the Soviet Union but guaranteed employment drastically reduced crime.

is this real or are you people like that guy in the dr strangelove movie launching nukes over fluoride?

Abortion. Low income women are more likely to have unwanted children. These children who would normally grow up in bad environments are being aborted as an alternative in these developed countries.

source: Freakonomics the book.

when you say crime, i assume you mean violent working class crime.

the rich and capitalists and the state rob more people and commit more crimes than the workers of the world ever could. But they make and enforce the rules, so they do not apply.

motherjones.com/environment/2016/02/lead-exposure-gasoline-crime-increase-children-health

It turns out the diminishing levels of atmospheric lead have correlated almost directly to decreasing levels of crime of all types.

Legal abortion

en.wikipedia.org/wiki/Tetraethyllead
Real enough that your parents breathed it.

Is Freakonomics actually any good? I often see it in book stores and have always dismissed it as gimmicky, pop-economics, neoclassical garbage.

This
Decreased crime isn't always as great as it seems. Cops acting more trigger happy can decrease crime too, as they don't usually convicted and it makes people more afraid of getting caught.
It's still mostly for mostly positive reasons probably (I hope)

I read an artile which said that in the UK at least most of the decrease in crime over the last twenty years or so has been in the form of the near dissapearance of violent crime from middle class areas wheras the crime rates in working class areas have decreased by only a very small amount.

You're conscious that 99% of people who haven't been "brainwashed" by liberals in college/media want all criminals dead right?
From petty-bourgeois sheltered lolbergs to evangelic christfags if you've broken da law you're no better than a dog.
I don't know about where you live but that's my experience.
Capitalism is pretty good at conditioning people to this kind of bootlicking.

I haven't read it either. I've also assumed it's garbage.

It gets better. From your link:

plenty of libruls think like that too

i actually remember when unleaded wasnt mandatory, i didn't say lead being in gasoline wasn't real, just the correlation with crime. what about crime before worldwide leaded gas use?

Tell that to all the rape and shanking victims in prison.

But prison population decreased along with crime in Europe…

I don't think it's possible to ever compare crime now and crime before the 20th century in detail because there simply wasn't any reliable (if any) statistical survey of crime back then. The closer I got to such a thing was in a socio-history book where the author insisted inter-personal violence was still part of everyday life in 19th century Europe, much more so than we could imagine it to be today.

The war on drugs.

In the developed world, most people are against the death penalty for anything that's not murder, rape or pedophilia.

I'm assuming you're brazillian, though. I know people are a bit more savage about that over there than in other places.

Abortions have lowered the amount of unwanted children who would have been raised terribly.

Welfare and mass media keeps people complacent, with no desire to take chances with crime or do anything, so the only issue is the rising levels of anxiety and depression due to absolutely no purpose in peoples lives anymore, leading to heaps of people taking antidepressants and then occasionally a person on SSRI's doesn't take their medication for a couple of days and goes on a spree. Or someone goes on a spree as their mind isn't compatible with living in the mass delusion.

Has there been a worldwide decline? Where are the stats?