Yes, lead poisoning could really be a cause of violent crime

[happyslug]

69. The rate of people being Killed in Europe in 1946 was a HUGE DROP from from 1944

Was lead involved in that drop? Or was some other factor the cause for the drop in then number of people being killed? i.e. the end of WWII. You have to control for drop in any death rate (and violent crime) if something else is clearly the cause of that increase or decrease. All studies have to do it, otherwise the results are useless.

Another factor that must be controlled for is people moving from areas of high culture of violence (The rural American South for Example) to areas of much lower rates of violence (The urban centers of the American North prior to 1960). People tend to forget that most urban areas, prior to the 1960s, had lower then average murder rates. The reason was simple, the rural South had much higher rates of murder and brought the National Average up. Thus this factor has to be controlled, i.e. compare groups with the same rates of murder and exclude groups where the change in murder rates can better be explained by massive immigration of people with a culture of different murder rates (i.e. African Americans moving from the Very Violent Rural South to the Northern Inner Cities starting in the 1920s to the 1960s).

You have to control for both of the above and any other factor that comes to light (including local crime wars such as the Crack Cocaine war of the early 1990s).