Archive for category Fun With Numbers

Correlation, Causation, Violent Crime and Guns

Perhaps you’ve come across this argument recently: The UK has a higher violent crime rate than the USA. And you know what else they have? Gun control! The argument hinges on a simple pair of coincident facts and a not-too-keen “connection” between them. Basically, the idea is that the violent crime rate is higher in the UK than in the USA because, in the UK, people don’t have guns to protect themselves. Further, a criminal in the USA doesn’t know whether or not a potential victim is carrying a firearm, and subsequently, is more cautious about attacking. In other words, the argument is you’re safer if there are no laws prohibiting or limiting gun ownership or where said guns may be carried.

Yes, it is true that the UK has gun prohibitions that the USA doesn’t. Does that explain the violent crime rate difference? What other correlations exist between the two countries? Well, the UK does have national health care and the USA doesn’t. Also, they love soccer and rugby instead of American football and baseball. Maybe that’s it. No wait, maybe the correlation is the number of non-white heads of state. (Sound of exploding conservative brains.)

The thing is, far from being an argument against gun control, this factoid is a very strong argument in favor of it. Consider two societies that are similar in many respects: a common language, a shared history, the same economic system, similar political systems, similar distribution and consumption of books, films, video games, etc., yet one country appears to have higher violent crime rates. The interesting rub is that this is not an across-the-board rate. While a rough estimate puts the overall violent crime rate in the UK at twice that of the USA, gun related homicides are roughly 50 times greater in the USA than in the UK. All other factors being equal, one would expect the gun-related homicide rate to echo the overall rate but this is not what we see. Clearly, though, all other factors are not equal. And what’s the most unequal factor? Why, the fact that it is very difficult for individuals in the UK to get their hands on firearms as compared to individuals in the USA. In other words, even if you have a desire to commit a violent crime with a gun, if you can’t get your hands on one, it becomes extremely difficult to pull that off. In other words, it’s an effective deterrent to said crime.

While it is true that some places in the USA have strict gun laws, the USA has never had sweeping country-wide laws regulating gun sales and gun ownership at anything beyond a token level and/or for relatively short spans of time. It is hardly “gun control” if, for example, a city bans handguns outright but with a short 10 minute drive to a neighboring state you can purchase firearms of a vast quantity and variety. This sort of patchwork is not the situation in the UK.

So it seems to me that an (admittedly imperfect) experiment has been performed. We have two similar societies. One has strict gun laws while the other does not. The one with the gun laws has a gun-related homicide rate that is 2% of the country without. This is not rocket science.


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Today’s Thought on Kinda Big Numbers

If you look up at the sky on a clear night away from obstructions and light sources, you will see a beautiful wash of stars. An awful lot of them, right? It has been estimated that a typical human can see a few thousand stars under such conditions with the unaided eye. This is out of the 100 billion or more stars in the Milky Way Galaxy. So, what’s the comparison?

Imagine that for every star you see, there is an entire night sky worth of stars. Now imagine that for every star in your new super-crowded night sky, there’s an entire night sky worth of stars again.

Chances are, you’d still be a little short.

And don’t forget that the Milky Way is just one of over 100 billion galaxies.

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A Lot of Money

Like many scientists and engineers I deal with very large and very small numbers daily. Sometimes, though, it is easy to lose perspective. Whenever I want to get a more visceral grasp on the relative size of something I make a similar ratio using stuff from the everyday world.

Consider money.  You can map quantities of currency onto scalar distance to get a feel for just what constitutes a lot of money. Suppose one US dollar is equivalent to half of an inch. That’s a little less than the diameter of a dime or about the diameter of a AA battery. So $1000 would be 500 inches or a little over 40 feet (nearly 13 meters).

What’s a lot of money for most folks? How about one million dollars? It’s about 20 times the median annual household income in the US and noticeably larger than the “nest egg” most people hope to retire on. Well, a million dollars equates to roughly eight miles in this scheme. A dime versus eight miles. Pretty big, right?

Contrast this to a billion dollars. A billion dollars is roughly the diameter of the Earth. So, think of how wide a dime is and then think of how wide the Earth is. That’s a billion to one ratio. Now there are people on this planet Earth who are billionaires. For example, the Koch brothers and several members of the Walton (Walmart) family are each worth in the neighborhood of 20 billion dollars. That’s 20 or more Earths lined up side-by-side. In comparison, if you have $100,000 in the bank, that’s equivalent to about 1400 yards.

At this point it is worth noting that the Supreme Court has pretty much said that money equates to free speech. So how loud do you think your voice is now?

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