A *Continuum* of Public Health

After writing my previous post on "public health", I realized that rather than a taxonomy it might be more useful to think about different dimensions on which these problems can vary.

1) You can easily limit the harm to other people.

2) You can easily limit the harm to yourself.

3) Contagion, non-linearities, and tipping-points are important or not.

Take normal driving and contagious disease as two examples of my "type 4" public health problems. You can't easily limit the harm you cause to other people, and you can't easily limit the harm to yourself, because giving up driving and becoming a total shut-in are extremely costly options. But in the case of driving, the problem scales linearly with the number of drivers. Twice as many drivers, twice as many accidents. Sure, there can be non-linear effects like traffic jams that basically never happen below some threshold. But you don't get one gigantic society-wide super-accident when you cross some threshold of X drivers. For epidemic disease, there are tipping points and herd-immunity effects. Vaccinating Y% of the population could dramatically reduce the spread of disease, not just reduce it by Y%. Creating a "fire-break" by vaccinating an entire geographic region could conceivably contain the disease. 

I think I made it pretty abundantly clear in my previous post that things don't fit neatly into tidy categories. I still think that the term "public health" is overused and essentially without value. It's like a magic phrase that conjures policy implications out of thin air, at least in the mind of the speaker who utters it. Before diving into policy implications, it's important to clarify that some people are consenting to these kinds of risks or deliberately engaging in some kind of self-harm. There are important moral and practical differences between self-harm and harming third-parties; likewise there are important differences between the consensual and the non-consensual. When people blurt out "Public health!" they are ignoring (perhaps deliberately) these considerations.

I anticipate that someone will take my "continuum" framing as some kind of concession. "Ah ha! Everything is kinda sorta public health, because every kind of self-harm kinda sorta has external costs, even if they are incredibly small." This is the kind of thinking that I want to resist. Perhaps obesity and smoking aren't just self-harm. Maybe the prevalence of these things causes people to find smoking and unhealthy eating socially acceptable, thus leading to more smoking and obesity. Perhaps second-hand smoke is a bit more harmful than we realize. I still resist the "public health" label for these kinds of things because doing so obliterates the notions of consent and free choice. If we can slap limits on each others' behavior for every minor annoyance (say, because my smoking increasing the odds of your becoming a smoker by 0.1%, or because your obesity has a similar effect on me), then none of us are really free. I think that below some threshold, it's meaningful to say that some things are private health and should not be subject to public policy. Conceding that the threshold is fuzzy and sits somewhere on a continuum is very different from pretending that threshold doesn't exist at all.