Open Source Defense

How to think about self-defense: tips from the world of personal finance

January 18, 2019

In the past two years I’ve been asked for more and more recommendations about matters of self defense and personal security, especially from urban, educated professionals who aren’t necessarily comfortable with firearms and who are definitely not used to thinking about their fellow citizens as potential threats to themselves and their families. For a variety of reasons, both valid and vastly overhyped, ordinary people are increasingly concerned for their physical safety.

There’s a standard talk that I give my friends and family on this topic, and I want to share it, here, because it’s critically important that folks who are new to this topic begin in the right place — not with a list of what things they should buy or skills they should acquire, but with a big-picture sense of how they should approach this entire topic of personal security.

Given the aforementioned demographic of people who ask me about personal security, there is an analogy that they often have prior familiarity with that’s a near-perfect fit for the problem of keeping yourself safe: personal finance.

Both self-defense and finance share the peculiar quality of information asymmetry: they’re complex fields where experts and insiders know a ton that normal people simply can’t grasp without becoming experts  themselves. On a practical level, that manifests itself in five important similarities that are worth pondering as you approach this topic for the first time.

Everyone’s situation is different enough that details matter

Most professional people who take some care with portfolio advice are aware that while there are general rules of thumb that work for most people, the particulars of their own situation — age, income, retirement expectations, geography, and health needs, to name a few — matter a very great deal for long-term financial planning.

It is exactly this way with personal security. Simple searches online will quickly net you some very general advice that’s worth heeding for most people, and I’d encourage you to evaluate such advice using the caveats and cautions laid out in the rest of this article. But detailed advice on equipment and training always has to be evaluated carefully with an eye to your specific situation.

Take the topic of guns — they are absolutely not for everyone. Some people live in states or countries where the legal risks and burdens of gun ownership are too high; others have home situations that guns simply do not belong in; and others will just never be comfortable with firearms. For these people, some mix of martial arts training, less-lethal weapons like mace or tasers, and finely-honed situation awareness might be the best option. Or, maybe the best they can do is get a large dog from a reputable breeder, and install some sturdy locks and ample outdoor lighting on their property.

If you’ve decided that guns are part of your security picture, then you have a whole host of specialized considerations to contend with. Will you be carrying concealed? How will you secure a firearm in your home? What guns are legal in your locality? Under what precise conditions can you legally use deadly force so as to minimize civil and criminal liability (this varies greatly by state in the US)? How often can you train with the weapon? And so on.

You can see how quickly the process of identifying your needs and then figuring out how to meet them gets complicated, which brings me to my next recommendation.

Seek out personalized instruction from credentialed advisors

If you can afford it or have access to the right person in your network, get professional help for as many aspects of your personal security as you can, just like you would if you were doing estate planning, buying life insurance, or investing for retirement.

The need for quality help is especially acute if you buy a firearm — you must seek out qualified instruction with an instructor who’s credentialed by a widely-regarded organization, whether that’s an NRA certification or something else. But even absent any gun-related considerations, consider finding and engaging a local private security professional of the type you can find in most cities to walk you through the basics of keeping yourself safe in your area of your city without exceeding the financial and physical resources that you reasonably can dedicate to this. Private investigators are also a good resource, here, if you can’t find local private security professionals.

Note: Beware advice from cops and former military, because not all of these people have quality training and directly relevant security experience. Just because someone had some weapons training for their day job doesn’t make them an expert on keeping you safe. Just as you would if you were interviewing a financial planner, check credentials and certifications, and ask tough questions about what this person actually did in their previous role.

Hustlers and scam artists are everywhere

For every Warren Buffett there’s a Bernie Madoff out there looking to scam the unwary out of their hard-earned money. And as rife with con artists as the world of money men is, the “tactical” and martial arts worlds are even worse.

You can’t swing a dead cat on the internet without hitting a former super-elite special forces operator who did three tours and was personally responsible for killing 15 of the last 20 guys we’ve claimed are “Al Qaeda’s number 3 operative.” Or so they’ll tell you.

If you go to a Krav Maga gym or BJJ school, ask about the instructor’s qualifications and lineage. Ask to see the framed copies of certifications that should be on on the wall somewhere. And if those copies are in a foreign language, take cellphone photos and run them by someone who can read them. (I once heard of a Chinese restaurant menu being passed off as a certificate in a Kendo dojo — it’s not even the right language.)

If you’re training with guns, then you have to be extra careful. Don’t just find out if the instructor is credentialed, but check up on them. Call the place where they said they’ve trained and see if there’s a record of them training, there. I regularly see YouTube videos of “trainers’” dangerous, showy stunts being circulated for criticism in some FaceBook groups I’m in. Don’t get taken in.

Watch out for folklore masquerading as science

Did you know that an AR-15 bullet was designed for wounding the enemy, and not killing them? You probably did know this, because everyone knows it, and it’s wrong.

If you want to learn about the actual science that went into the design of the AR’s 5.56 NATO round, then there are books that summarize and even reprint some of the McNamara-era Department of Defense studies that gave rise to the gun, but most folks (including too many who should know better) are content to pass along tactical folklore about wounding Viet Cong and piercing Soviet-era metal helmets.

Similarly, I often see claims about bullet calibers and “stopping power” and “rules” about attack distances that are couched in scientific terms but haven’t necessarily been scientifically evaluated. In short, as is the case with some “technical analysis” and stats and charts that personal finance gurus publish for viral clicks, just because it sounds like science doesn’t mean it’s science. As always, do your own homework.

Every hot tip you get from friends and family is probably wrong

Back in 2013, former Vice President Joe Biden got into hot water for advising people to buy a double-barreled shotgun and fire off two rounds into the air to scare off intruders without harming them. The problem: that terrible but alarmingly common advice could get you either killed or arrested.

I can’t count the number of times I’ve heard someone offer up a Louisville slugger stashed under a carseat as a superior alternative to a firearm for home and auto defense. This blustery bit of vigilante fan fiction is typical of the advice you find online. A bat is certainly a valid option if you’re gun-shy, or even a possible backup option if you aren’t, but superior to a firearm? No. When you, untrained civilian, whack a 250-pound attacker wearing a heavy coat in the wrong place with your mini-slugger, and he grabs it from you and goes to work on you with it, you’ll spend your final moments wishing you had a gun.

Just like you don’t jump on random hot stock tips from people on the internet or friends and family (at least, I hope you don’t), avoid these simple-sounding self defense tips, where somebody confidently lays out the One Cool Trick They Don’t Want You to Know for keeping yourself safe.

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A live list of Second Amendment court cases to watch

December 30, 2018

For the past couple months, we’ve maintained a private spreadsheet of important active cases at the circuit court or Supreme Court level. Just realized it could be a useful community resource, because no similar snapshot seems to exist anywhere else. So it’s now public at the link below. Anyone logged into Notion can comment — let us know if there are any cases or details we’ve missed.

Second Amendment court cases to watch

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Second-order thinking about gun rights: handy articles and videos

December 28, 2018

For the familiar points of disagreement, most people (on all sides) resort to first-order thinking and low-effort culture war agitprop. That provides short-term validation, but it doesn’t spread knowledge and it’s not persuasive to those who disagree.

To persuade and to get smarter ourselves, it’s important to focus on systems-level thinking. Here’s a list of highly shareable, high-quality answers to the issues that frequently come up around gun rights.


The Rifle on the Wall: A Left Argument for Gun Rights

Everybody’s Lying About the Link Between Gun Ownership and Homicide, and the rest of BJ Campbell’s gun series

A Guardian study showing that murders in the US are extremely concentrated to specific areas and demographics, which suffer under rates of violence an order of magnitude higher than the median

Why I “Need” an AR-15

Confessions of a Progressive Gun Nut

The Path Forward on Guns, and its explanatory Twitter thread


Alan Korwin answering the question “Why do you need an AR-15?”

Korwin also level-headedly addresses the subtle inherent flaws with the idea of gun registration (he doesn’t use the term “base rate neglect”, but nicely encapsulates the concept):

The Feed, “Gays & Guns”:

BuzzFeed, “Grandmas Shoot Guns for the First Time”:

Keanu Reeves at the range:

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Base rate neglect and Andrew Ross Sorkin’s credit card surveillance system

December 28, 2018

The New York Times’ Andrew Ross Sorkin published an article on Christmas Eve, to argue that credit card companies should build models that take spending activity as input and return “probability that this customer is planning a mass shooting” as output.

An excerpt from the crux of it:

A New York Times examination of mass shootings since the Virginia Tech attack in 2007 reveals how credit cards have become a crucial part of the planning of these massacres. There have been 13 shootings that killed 10 or more people in the last decade, and in at least eight of them, the killers financed their attacks using credit cards. Some used credit to acquire firearms they could not otherwise have afforded.

Those eight shootings killed 217 people. The investigations undertaken in their aftermath uncovered a rich trove of information about the killers’ spending. There were plenty of red flags, if only someone were able to look for them, law enforcement experts say.

Sorkin is well-known for having used his NYT column in the weeks after the Parkland massacre to successfully lobby Citigroup and Bank of America to fire their business customers who sell standard-capacity magazines and other common touchstones. So people on all sides reacted predictably to his new article.

Some people loved the idea:

Civil liberties advocates and gun rights advocates were, as a rule, less sanguine:

The philosophical disagreements are well-known to anyone who has studied them, and I won’t rehash them here beyond saying that Jonathan Haidt’s moral foundations theory captures it well (particularly the theory’s care/harm, authority/subversion, and liberty/oppression axes).

That can be a fun discussion to have, but it’s not one that’ll teach us anything new. Instead, we’re going to examine something that almost everybody missed: the straightforward innumeracy of Sorkin’s article.

Base rate neglect is a simple and counterintuitive idea: the chance of a test giving a false positive is determined both by the test’s accuracy and by the prevalence of the condition that the test is looking for.

Wikipedia explains, using a hypothetical terrorist detector machine (lightly edited here for brevity):

In a city of 1 million inhabitants let there be 100 terrorists and 999,900 non-terrorists. Thus, the base rate probability of a randomly selected inhabitant of the city being a terrorist is 0.0001, and the base rate probability of that same inhabitant being a non-terrorist is 0.9999. In an attempt to catch the terrorists, the city installs an alarm system with a surveillance camera and automatic facial recognition software.

The software has two failure rates of 1%:

  • The false negative rate: If the camera scans a terrorist, a bell will ring 99% of the time, and it will fail to ring 1% of the time.
  • The false positive rate: If the camera scans a non-terrorist, a bell will not ring 99% of the time, but it will ring 1% of the time.

Suppose now that an inhabitant triggers the alarm. What is the chance that the person is a terrorist? In other words, what is P(T | B), the probability that a terrorist has been detected given the ringing of the bell? Someone making the “base rate fallacy” would infer that there is a 99% chance that the detected person is a terrorist.

The fallacy arises from confusing the natures of two different failure rates. The “number of non-bells per 100 terrorists” and the “number of non-terrorists per 100 bells” are unrelated quantities. One does not necessarily equal the other, and they don’t even have to be almost equal. To show this, consider what happens if an identical alarm system were set up in a second city with no terrorists at all. As in the first city, the alarm sounds for 1 out of every 100 non-terrorist inhabitants detected, but unlike in the first city, the alarm never sounds for a terrorist. Therefore, 100% of all occasions of the alarm sounding are for non-terrorists, but a false negative rate cannot even be calculated. The “number of non-terrorists per 100 bells” in that city is 100, yet P(T | B) = 0%. There is zero chance that a terrorist has been detected given the ringing of the bell.

Imagine that the first city’s entire population of one million people pass in front of the camera. About 99 of the 100 terrorists will trigger the alarm—and so will about 9,999 of the 999,900 non-terrorists. Therefore, about 10,098 people will trigger the alarm, among which about 99 will be terrorists. So, the probability that a person triggering the alarm actually is a terrorist, is only about 99 in 10,098, which is less than 1%, and very, very far below our initial guess of 99%.

We can apply the same math to estimate a false-positive rate for Sorkin’s mass shooter detector. We’ll make a few assumptions about inputs, in each case being maximally generous:

  • False positive rate of the credit card company’s machine learning system, with respect to mass shooters: 1%
  • False negative rate: 1%
  • Number of people using a credit card to make any gun-related purchase in a given year: 25 million. Pew estimates that 30% of American adults (just over 75 million Americans) own a gun. We’ll say that only one-third of them make any gun-related purchase (any ammo, guns, or accessories whatsoever) on a credit card in a given year.  That’s very likely to be an underestimate, but we’ll stick with a low number because that’s more generous to Sorkin’s model.
  • Number of credit-card-using mass shooters per year: 4 (Sorkin’s article identified 8 such murderers over 11 years, so 4 per year is a much higher estimate that is again maximally generous to Sorkin.)

Running these inputs through the math above, we find:

  • Given the 1% false negative rate we’ve assumed, the system will flag ~4 true positives per year.
  • Given the population of 25 million purchasers and a false positive rate of 1%, the system will flag 250,000 false positives per year.
  • Therefore for every true positive, there will be 62,500 false positives. In other words: when the system raises an alarm, there is a 99.9984% chance that the system is wrong.

Remember also that our input numbers are unrealistically generous. False positive and false negative rates around 1% are achievable in tightly defined circumstances. Physics models, narrow subsets of medical imaging, and the like.

In predicting human behavior, 1% error rates are unheard-of. Companies like Facebook get paid billions of dollars to build these systems, and they hire armies of elite PhDs with unlimited resources to do it — and they’re regularly on the front page of Sorkin’s own newspaper for messing it up. In the real world, double-digit error rates abound.

An automatic response might be, “62,499 — or 10x that many, or 100x — false positives will be worth it if the system catches one true positive.” But that elides the core problem that we set out to solve: you don’t know ahead of time which one of the 62,500 (or 10x that many, or 100x that many) is the real mass murderer. And there is no system that can sort through that haystack without running out of resources (having first consumed all the resources that the system was built to save in the first place). Human reviewers can analyze the ML model’s flags, but at the cost of increasing bias and false positives — worsening the very problem they’re trying to solve.

Base rate neglect is counterintuitive, but famous enough in the ML community that well-informed people expect a famous reporter to know about it before writing a NYT feature.

This would be like writing an article criticizing Amazon for burning jetfuel instead of teleporting packages — interesting to debate, but surreal to do so without ever mentioning that the technology for teleportation doesn’t exist.

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