20% still seems overly high to me there are so many compounding individual factors related to lead exposure itself.
The effect of lead on an individual has a great deal of variability; age/size of the individual concentration of the exposure, duration, variation of serum lead levels within affected dwellings.
When it comes to Rome I always get the sense that once we have a good grasp of a modern problem, we start post-hoc fitting it to an old mystery. I see this a lot in paleontology and astrological theory. Too often I see scientific theory including greenhouse effect into absolutely every disaster scenario. Once we have a good scientific grasp of an issue I think theorists start seeing it everywhere. That is just my opinion. I am not advocating ignoring the lead problem. I am concerned that this type of hypothesis distracts people from the major factors affecting crime ridden area’s. Lead abatement is a relatively easy problem to deal with compared to poverty and community violence.
Interesting, but this type of behavioral link always makes my skeptical spidey sense twitch. Sometimes inappropriately.
locutus – I agree, but this is the information I found. I don’t know how reliable the 20% figure is, but I do note it dates from the peak of crime in the early 1990s, which means it is probably a smaller contribution to today’ crime. (taking all this at face value).
In any case, as I said, that still leaves 80% or so due to other things.
If we take the narrow question – should we invest money in reducing lead in the environment, I think the answer (even giving the uncertainties in current data) is yes. But as always let’s also track the results.
Good post. I’d like to see a comparison with other variables over the time period (60′s to today). Most likely they are sociological, such as household income, single-parent families, social cohesion, drug trade trends, legal regimes, etc. However, there must be other chemicals that are neurologically harmful that rose and fell over that time period as well. If such a source was found, and it very closely correlated with leaded gasoline use, would that mean the two together would account for about 20% of the variation or could the two together account for more using the same framework?
Oh a chance to remind Steve that for some toxins the dose, whilst important, doesn’t make the poison, since no safe dose has been established for lead exposure (or Ionizing radiation, and a handful of other poisons). Can you tell that expression bugs me?
Heptron – wikipedia has a great article on lead poisoning.
The effects of lead are myriad, it has no known (positive) role in physiology. I believe the big concern are over fetal and early childhood development, one study (Schwarz J 1994) showed 2.6 IQ points dropped for each 10 mg/dl in blood serum. That said this is a lot more lead than one would hope to find in one’s blood, only 7% of US school kids had more than one thousandth of that much lead in one study. So whilst I’m keen to point out no safe level has been established, the levels found in most people since lead was removed from petrol are not a significant health concern.
The use of graphs in the original article is I think misleading, and something we should as skeptics be wary of (and critical?). They’ve shuffled axises both vertical and chronologically to overlap two peaks. If we are allowing overlaying such graphs, then this one is much more convincing.
Clearly one would expect a delay between childhood poisoning and adult criminality, but since lead affects the brain’s development, and people went through exposure at different times, and typically don’t suddenly become non-criminal (unless imprisoned) the effect should be more spread out in time than the cause. Since the graphs suggest a more immediate overlap they are probably evidence that lead had a very small or no effect on crime levels, and any correlation of the graphs is probably because of the way they have been scaled and manipulated rather than due to any effect from lead. In this case correlation implies lack of causation (I must get extra skeptic points for that).
For all compounds exhibiting toxic effects there is a dose response curve.
In the low dose regime, the effects are from the hormetic distortion of the normal regulation of physiology. For that, there is no threshold because the pathways that are normally regulating physiology to be a certain way are already in the active range, so perturbing them moves them to a different operating point of that active range.
We know there are physiological pathways that regulate the degree of violence an individual exhibits. Exposure to violence increases this, as in the cycle of violence. That is most likely mediated through pathways activated during fight-or-flight. A final common pathway is very likely oxidative stress. Lead does cause oxidative stress, so it very likely does couple to other pathways controlled by oxidative stress.
Steve Sailer gets 0 points for dealing with Nevin’s paper. He doesn’t seem to understand that regardless of the age cohorts chosen or resolution thereof, the variation in crime rate is predicted very nicely (uncannily, in fact) by time lagged lead exposure.
Also, he keeps talking about this whole “60′s freak out” thing which is irrelevant: the relationship is not weakened because it doesn’t account for some portion of the data you pick out of a hat as important. Predicting variation in some dependent variable (dv) from some independent variable (iv) does not mean that peaks, troughs, etc are somehow more important than any other part of the dataset. Obviously if the two are related, as one gets up the other tends to, but there are clearly other forces at work on the DV, so the lack of explanation of prediction of some peak X does not invalidate the statistical relationship between the 2 variables. Especially considering the political upheaval of the time that was also influencing behavior.
He also avoids a lot of the other geo localized lead exposure evidence that does show a relationship. Ignoring evidence is his strong suit.
IOW, nothing he writes really refutes the data in Nevin. Nevin has either screwed up (possible) or there is another variable that rises and falls with lead exposure.
This could be due to the fact that Sailer has a dog in the fight, i.e., he is a racist ass hole. Sailer believes that blacks are genetically less intelligent than whites, so he needs to argue that environmental factors, epigenetic factors, etc. are not explanative in testing differences between races (of course intelligence is linked to criminality). He seems reasonable when you read him, but he ignores a shitload of data he doesn’t want to deal with to maintain his racist ideology, which is ugly unscientific nonsense.
Of course this isn’t WHY he’s wrong re: Nevin. He’s wrong because of what I wrote above. But the reason he makes those arguments, IMO, is because he’s a racist ass hole. Lest someone accuse me of ad hom reasoning….
There’s some confusion above about claims re: % of violent crime accounted for by lead. Nevin was reporting coefficient of determination (called R squared, literally the r value squared) which tells you the proportion of variability of your DV that’s accounted for by you IV(s).
Nevin did indeed find that 90% of the variation (R squared =.9) in violent crime was accounted for by variation in childhood lead exposure, but this is not nearly the same thing as saying that 90% of crime is caused by lead exposure. We’re still looking at a correlation, so other factors that changed with lead exposure could be at play. Many things were improving in society over this time period, including exposure to other toxins, better teaching methods, etc.
Another issue is that we’re we’re modeling the change in crime over time around some baseline. You could have a baseline crime rate (with many causes) that would be present no matter what, but we’re modeling the variation around that baseline over time, so it would be wrong to claim that this finding is accounting for the percentage of all violent crime. It’s modeling the change in crime rates over time, which is different thing.
That said, the number IS really high, and does raise a furrowing of the brow to be sure.