By now you’ve probably seen this chart. It can be read in a couple of different ways. One way is to see that the rising rates of Autism diagnoses is correlated with increased sales of organic food. But we still don’t know the true causes of Autism and so the more entertaining way to read this is that organic foods cause Autism.
Our monkey brains always want to connect two similar trends and have one explain the other. Organic food sales are a clear reaction to increased Autism diagnoses but who’s to say the correlation doesn’t go the other way? As the popular media have embraced publishing results of “studies” we’ve come to rely on the skeptical line of “correlation doesn’t equal causation”. This allows us to dismiss wild claims based on correlations. The chart above perfectly illustrates that. But saying correlation doesn’t imply causation also lets us dismiss something simply because we don’t want to believe it.
Case in point: Over the last year a popular idea has emerged to explain the dramatic drop in violent crime we’ve witnessed over the past few decades. You can see the trend on a chart here. Many have tried to explain various policies or changing demographics as the reason behind the drop in violence, but nothing has ever been all that conclusive. But now a very simple explanation is emerging.
Yep, good ole chemical element Pb. Lead can be very toxic to humans, and the effects of lead exposure can affect our brain and nervous system in ways that can lead to making us more likely to engage in violent behavior (among many other things, including death). Lead used to be in everything from paint to our gasoline and so lead exposure, even on a small scaled, was very common. We tend to think of toxic exposure as having an bedimmed effect, but subtle exposure over a lifetime (like a cigarette) can do the most damage. Below is popular chart showing lead exposure in the environment and the overall violent crime rate 23 years later.
Based on this chart, lead exposure seems to be a fairly strong predictor of violent crime. “But correlation doesn’t mean causation”. And that’s absolutely right. Thankfully, we have more rigorous tools to test statistically how strong the relationship is; said another way we can test of the correlation is a coincidence or not. And the number seems to pass the sniff test. However some criminologists are dismissive of this new data. Not seemingly because of the “correlation”, but in spite of them. So the correlation/causation argument gets floated around quite a bit.
Sadly, or thankfully depending on your perspective, we don’t have a way to truly test the long term effects of lead exposure on a society. So there’s no pure way to isolate lead as a factor and truly test it. But to simply ignore a possible environmental factor because you hadn’t thought of it is bad science. Something like the lead exposure theory at least deserves more research.
Coincidentally, the television show “Cosmos” followed a similar story arc just the last weekend where lead toxicity was discussed. In this episode, the host explains that some researchers believe that part of the reason the Roman empire fell was due to their use of lead in plumbing. In fact, the English word “plumbing” comes from the Latin “plumbum” (hence the element: Pb).
So drink up.
Further reading: Did removing lead from petrol spark a decline in crime? (BBC News Magazine)