Public Health: A Taxonomy

Different kinds of things that are all lumped together as “public health.”  Here is my list of categories in an arbitrary order and with an arbitrary naming convention. Admittedly these categories are fuzzy and potentially ambiguous, as I will discuss below:

Type 1: Your behavior harms you and nobody else. (obesity, smoking, alcoholism's effects on your own body but not drunk driving)

Type 2: Your behavior harms other people, but they can reasonably avoid the risk. (communicable diseases through intravenous drug use or casual sex, smoking in bars)

Type 3: Your behavior harms other people. You can make decisions that will avoid harming others, but the injured parties can’t reasonably avoid the risk. (drunk driving, pollution)

Type 4: You cause harm to other people, but neither you nor they can do anything reasonable to avoid the risk. (epidemic diseases, normal driving, some kinds of pollution that everyone basically consents to tolerating)

I despise the sloppy use of the term "public health" because I think it's misleading. Usually the word "public" somehow means "my behavior effects you" or "this is an intrinsically collective decision." Economists use the term "public goods" to describe things that are under-produced because most of the benefits accrue to the public rather than the producer. And "public bads" (or "externalities") are things for which most of the cost is borne by the public rather than the producer. (Pollution, reckless driving.) These things are over-produced. In fact, economist will say things like, "Public goods are under-produced because the public benefit exceeds the private benefit." There is this explicit distinction made between public and private, at least in the language used by economists. When people say of some crisis, "This is a public health issue!" there is often nothing public about it. What they really mean is that they are looking at a private problem and counting instances of it across a large population. If Johnny eats too many sugary snacks and grows obese, that is not a public health issue. If there are tens of millions of people just like Johnny, it still isn't a public health issue. It's a private health problem summed across a population.

Many things fit into my Type 1 category. Obesity is bad for you, but not especially bad for your neighbors. Smoking mostly harms the smoker. There are some disputed studies on the harms of second-hand smoke, and the harm is surely real. But it's at least an order of magnitude smaller than the self-harm that the smoker does to himself. Any kind of risk-taking in which you don't endanger third-parties goes into this category. Drug use. Riding horses. Skiing. I don't think it's appropriate to call any of these things "public health" because the vast majority of the harm is self-harm (outside of some weird bull-session hypotheticals).

Type 2 public health is different. Your behavior is potentially harmful to other people, but they can make the decision to completely avoid the risk. Communicable diseases in IV drug users is certainly a public health problem. You can build contagion models and do network analysis to predict the spread of diseases. You can mitigate the problem with needle exchanges. You can disrupt the spread of disease by perhaps breaking the connections between different networks of users. If there are vaccines for some of these diseases, you can achieve herd immunity and fire-break effects to lower contagion. This has a very "public health" feel to it. But it's distinct from Type 3 and Type 4 in that anyone can choose not to be in the harmed population. Don't engage in IV drug use (and, presumably, don't have sex with anyone who does) and you've basically eliminated your exposure. Type 2 problems can be analyzed and mitigated using all the traditional tools of public health, but people can willingly eliminate the risks to themselves by not engaging in the risky behavior. Likewise, you can remove yourself from a smokey bar or a roller derby, or abstain from casual sex.

Type 3 problems are things like pollution or drunk driving. You are engaging in a harmful behavior, and the people who you are hurting can't reasonably mitigate the risk. It's unfair to tell someone they can simply avoid drunk drivers by not driving, in a way that it's not unfair to tell someone they can simply avoid HIV if they avoid intravenous drug use and casual sex. It's unfair to tell someone that they could have avoided cancer (or asthma or acute poisoning) if they didn't live near that factory that clandestinely pollutes more than the legal amount. (More on this below; some kind of pollution are unavoidable, and we all essentially consent to them.) There is a "bad guy" in this problem. There is someone harming unwilling third parties, and this someone could solve the problem by ceasing their harmful behavior. I think it's fair to label these problems "public health."

Type 4 problems are what I think of as true public health. There's really nothing you can reasonably do to avoid exposure to the risk, and there's really nothing the injuring party can do to avoid exposing you to it. Think of an airborne epidemic disease, or a waterborne disease in the era prior to modern sanitation. As I said in my previous post:

There isn’t necessarily a villain, just normal people going about their lives within a population exposed to some infection risk. These are situations where it’s nearly impossible to limit your own exposure to the risk or your contribution to the risk. The instructions for the former are “don’t breathe in” and the instructions for the latter are “don’t breathe out”. Or perhaps there is a less extreme possibility such as “become a complete shut-in,” but let’s suppose that’s so impractical that it’s not really an option for most people. These are the situations that truly justify a public policy.

I think of Type 4 as the purest form of public health. Type 2 is close behind, Type 3 next, and Type 1 isn't really public health at all, in the sense that it's not really public. Some people try to verbally convert Type 1 problems into public health issues by pointing out that some government program forces the rest of society to shell out for private mistakes. I'll briefly note that a policy change could convert these "public" problems back into purely private problems, and we should seriously consider making those policy changes.

What about opioid overdoses? I'll discuss pills and heroin separately, starting with pills. These are really Type 1 problems. People imprudently take too many pills, or take them with benzodiazepines and/or alcohol, or take them when they have a medical condition that exacerbates respiratory depression (sleep apnea, obesity). There is simply nothing "public" about it. You could possibly hand out fliers that meaningfully inform people of the risks (as I've advocated many times), and this might plausibly reduce the number of overdoses. But at the end of the day this is self-harm.

If we take the world as it is as a given, heroin overdoses are also a Type 1 problem. There are the Type 2 issues of communicable diseases discussed above. But the overdose risk is self-harm. Maybe some sleazy drug dealer cooks up a batch of low-grade heroin spiked with fentanyl and several of his clients overdose. Maybe the first time this happens it's a Type 3 problem, but once every heroin user knows this is happening it's more like a Type 2 problem. It's something that happens once in a while, and they could avoid the problem by avoiding their exposure to it entirely. Note the qualifier in italics that I began this paragraph with. Next I'll argue that this is a Type 3 problem.

Suppose we don't take the world as a given. Suppose we consider drug policy to be malleable. Under Policy 1, there will be 10,000 heroin overdose deaths a year. Under Policy 2, there will be only 500 heroin deaths a year. Perhaps Policy 1 is a strict regime of drug prohibition like the one in the United States. Perhaps Policy 2 is a regime of harm reduction, decriminalization, even legalization, like we see in several European countries. (Of if you like, perhaps it's the reverse.) Those heroin users are all consenting to some kind of risk. They are all exposing themselves voluntarily to some kind of hazard. (At least initially, before they are hopelessly addicted...if you buy the "drugs dominate the will" narrative of drug addiction.) But someone is causing them unnecessary harm. That "someone" is the voting public. Sure, heroin users consent to the risk in both cases. But in the case of Policy 1 the risk is much higher. (I nearly said "20 times higher" but this would make an unwarranted assumption that the using population is the same under both policies.)

Heroin overdoses aren't a public health problem because someone counted up the bodies across "the public." Heroin overdoses are a public health problem because bad policy has made heroin absurdly dangerous, more so than it would be under a saner drug policy. The bad guys in this story are the drug warriors and the apathetic/ignorant voting public. I'm okay with labeling a problem a "public health issue" if we're willing to talk seriously about how bad government policy has made the problem worse.

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I listed "pollution" as a Type 3 problem, but sometimes it's more like a Type 2 or a Type 4. Suppose there is a factory town. Everyone in town basically works in the factory, or somehow services the factory's workers. The factory emits pollution, which occasionally causes health problems in the community. But nobody wants to sue the factory, because everyone would be out a job if such a lawsuit actually won. This isn't some rogue capitalist secretly dumping waste into a river and poisoning everyone downstream. This is a case of a community consenting to a mild hazard because it's worth the cost. Maybe some people can choose to move away, so it's more like a Type 2 problem. Or maybe people are mostly stuck in the community because they don't have viable alternatives, so it's more like a Type 4 problem. I think auto pollution is more obviously a Type 4. It's hard to avoid being a contributor to the problem, and it's hard to avoid the effects of the pollution. You can try to mitigate it with policies like emission standards or congestion pricing. But with those things taken as a given, everyone pretty much puts up with the hazard. It's not something that one party "does to" another party. It's just a cost of living a life.