by Carl V Phillips
A correspondent suggested to me that those who are not population health experts have a gut feeling that all this rhetoric about “epidemics” — of tobacco use, of teen vaping, and such — is an innumerate misuse of the term. But few really understand why.
The first problem with these claims, which I think most people get, is that “epidemic” refers to a disease, and these behavioral choices are not diseases. Of course, words get used metaphorically, and it is a somewhat complicated technical term that thus has hundreds of pop-level dictionary definitions floating around. But keep in mind that the people misusing the word in this case are supposed health science experts: The WHO entitles its flagship semi-annual reports on anti-tobacco policies, “WHO report on the global tobacco epidemic 20xx”. The U.S. FDA has been banging on about an epidemic of teenage vaping. This misuse of the terms frequently appears in public health journals. This is not ok.
Yes there are colloquial common-language uses of the term that are not limited to actual diseases (and there are also those that are narrower still and use the word to refer to infectious disease outbreaks specifically). But health “experts” and officials should not be using sloppy colloquial definitions of technical scientific words. It would be like economists using “efficient” to mean “quick and effective” or geneticists using “fitness” to refer to someone’s cardio statistics. (In case you do not know, each of those is an important technical term in its field, with a particular meaning.) It it similar to a physician using “cancer” or “poisoning” metaphorically when talking to a patient — “I’m afraid that you have cancer…. Of your motivation, which is keeping you from really focusing on your physical therapy.” (I have a recollection of Dr. Hibbert on The Simpsons having a conversation in which he keeps saying things like this, alarming the family for a beat before he makes clear he is not really meaning the words. Anyone know how to find a clip of that?)
So that alone is a simple, obvious fatal error in this usage. Anyone misusing the word to refer to a behavior they dislike, rather than a disease, and doing so in the context of health science, is engaging in propaganda rather than an attempt at accurate communication. But even if we set that aside — ignore the inappropriate metaphor of calling a behavior a disease — the use of the term is still blatantly incorrect.
For a disease to be in an epidemic state, it needs to have an incidence rate that is not necessarily high, but that is spiking above the normal baseline. (It also needs to be affecting a fairly broad population and not have a single source of exposure, as often happens with foodborne disease, or we instead call it an “outbreak”. But that is not really relevant for present purposes.) So, even though there are always a lot more heart attacks and HIV infections compared to Zika infections, Zika has recently been epidemic in some populations, while the others were not. The big numbers for the others are (usually) just the normal incidence rate. Exactly what is enough of a spike to qualify as epidemic is not precisely defined, but it is safe to say that (genuine) experts would not call a sudden jump of merely 10 or 20%, let alone a steady upward trend with similar increases, an epidemic.
So is tobacco use a global epidemic (accepting the metaphorical non-disease use of the word), as suggested by the WHO? Clearly not. It is actually in decline. In almost every population, the prevalence of tobacco use and, more importantly, the incidence of initiation are declining. I am pretty sure that there is not a single country where the current increases in tobacco use would qualify as an epidemic, though I might have overlooked somewhere. If you drill down enough, undoubtedly there are some subpopulations with recent spikes that would qualify as epidemic. But you have to look hard, and it is clearly not global.
(Aside: The number of smokers in the world has continued to increase, despite the decline in incidence and prevalence. The population is increasing faster than smoking rates decrease in all but the substitution-miracle countries. And of course, “tobacco use” does not decrease when product substitution reduces smoking. In addition, in a few large populations — extremely poor people who finally have enough income to afford tobacco products — rates are increasing, though not at epidemic levels. Bottom line: do not get misled by tobacco controllers when they temporarily switch their rhetoric from “epidemic!!!” to “we are close to eliminating smoking!!!” They are not.)
But how about more specific claims like FDA’s “epidemic of vaping among U.S. teenagers”? For that claim, the metaphor is even more strained (and, again, clearly inappropriate coming from an ostensibly scientific health agency): At least smoking can be metaphorically likened to a disease because it causes a lot of disease outcomes and so is similar to not-yet-morbidity-causing cases of an often-harmful infection. But vaping and other smoke-free tobacco use are approximately harmless. Saying “vaping epidemic” is a lot like saying “Fortnite epidemic”; yes, I suppose you can metaphorically refer to a sharp increase in the initiation of any consumption choice, but when the serious disease risks are trivial, it seems like a pretty stupid choice. You should just go with “sharp increase”. Though in cases like these, where the sharp increase in consumption is inevitable because no one was using the product a few years ago, even that is kind of stupid to say.
Worse is that this is an example of the “look at just one entry in the ledger” game that tobacco control rhetoric is notorious for. Compare their game when they pretend that smoking costs society money by toting up costs of treating (frequently fatal) smoking-caused diseases, ignoring the (almost exactly offsetting) reduction in the cost of treatment for some later disease that never happened because the person died from smoking. They also ignore other foregone consumption (housing, food, etc.) that results from earlier deaths, which add up to meaning that smoking’s health effects cause an enormous net savings in social resources. It is the same game used by those who say we cannot afford single-payer healthcare because it would cost $X trillion, and we cannot afford that — never mind that we are currently spending 30% more than that on healthcare, and would save that cost. It is as if someone said “I would eat out less, but I could not afford the resulting increase in my grocery expenditures.”
In the present case, FDA et al. ignore the decline in teenage smoking that offsets (and is pretty clearly caused by) the increase in vaping. What they are saying is equivalent to breathlessly panicking that we are experiencing an epidemic of a specific influenza strain, even though we were having an unusually mild flu season. It just happens that the year’s dominant strain is a relatively new mutation and there had not been many inflections with this particular strain in previous years, even though influenza is almost always more common and more harmful than in the present year.
FDA’s carve-out logic also means we are also experiencing an epidemic of teens smoking Marlboros that were manufactured in 2018, even though smoking is way down. I mean, no one was smoking those just a few years ago, and now they are, like, everywhere! Something must be done!
In short, it makes no sense to talk about an epidemic of a single option within a category of competing diseases/products. The entire category should be considered. (Notice the trap here for the crowd who seeks to die on the hill of “e-cigarettes are not in the tobacco products category.” This is a way you could actually die on that hill.)
The final problem with the use of “epidemic” — even ignoring for the inappropriate strained metaphor, the full-on falsity of the WHO’s version the claim, and the misleading tricks behind FDA’s usage — is more subtle. It is a question of what counts as a population.
An epidemic occurs when there is a spike in cases, across time, within a particular population. We do not say that Congo has an epidemic of malaria because they have a much higher incidence rate than Canada, or vice versa for frostbite. The word someone is probably looking for there is “endemic”. We only say “epidemic” if there is an increase in the numbers within the country. However, this is not about the place, but the group of people. So who constitutes the population, the group of people to compare over time, for tobacco product use?
Unlike influenza, tobacco product use is all about cohort replacement. That is, flu incidence changes from year to year because a different portion of the (mostly) same population get the disease. By contrast, population smoking prevalence changes mostly because the new cohort that is being added to the count (e.g., those turning 18 that year) has a different prevalence than those dying that year. Yes, there is smoking uptake by 19- to 25-year-olds (though that is still really a matter of cohort replacement, and would be clearly that if we took those FDA et al. like to call “youth” out of the adult population and looked only at prevalence for age 26+). Yes, there is also quitting at all ages. But year-to-year changes are driven by an entirely different engine as compared to infections sweeping through a population.
Notice that I have had to distinguish incidence (rate of new cases occurring) from prevalence (portion of the population who have the disease/behavior), a distinction that seems to baffle tobacco controllers even though it is first-semester public health. They can never decide which one they consider to be important. Sometimes they whine about rate of trialing (incidence of first-trying a product). Sometimes they whine about ever-use (prevalence of ever having ever trialed the product; this, of course, can only increase for a cohort over time), without seeming to understand the difference. Currently FDA seems to be making their “epidemic” claims about “used at least once in the last 30 days” prevalence.
Among their and WHO’s more subtle crimes against the word “epidemic” is that that word refers to spikes in incidence rates, not in prevalence. Consider that the prevalence of HIV is far higher now than ever before (thanks to maintenance treatments that let people live with it). Is this an epidemic? Similarly, the population prevalence of HPV-16 will peak when the vaccines become sufficiently widely used (and thus in future years the new cohorts are immune while some of those with the virus are dying off). So does this mean that the epidemic will be at its height at a time when the incidence rate is hitting its lowest point since the start of the sexual revolution? The innumerate use of the word that FDA is employing would say exactly that.
But getting back to the question of populations, the problem is more subtle still. Consider the population “Americans born in 2000”. When looking for epidemic-level increases, can we look at that cohort’s own incidence rate of vaping or even (ignoring the fatal problem noted in the previous paragraph) prevalence of recent usage? That obviously does not work, because of course those will be higher in last year’s statistics than they were in recent years when that population were little kids. That is like saying we are experiencing a huge increase in knowledge of simple calculus, because so many more in that cohort know it now than a few years ago. Is someone also going to whine that there is currently an epidemic of premarital sex among Americans born in 2000? (We should certainly hope there is!)
Even though this is really the only comparison that makes sense for properly using the word epidemic, it is obviously dysfunctional and so is not the comparison that gets made. Instead, incidence rates (or, more likely, prevalences) are compared, year-to-year, among 17-year-olds (or for whatever age cohort). But this is not a comparison within a population. It is, in fact, an entirely disjoint population, like comparing Congo and Canada; those who are 17 on a particular date in 2017 include no one from the population who was 17 on that date in 2016. So you can say, e.g., that vaping among this year’s 17-year-olds is much higher than among last year’s (just as you can say malaria is much more common among Congolese than Canadians), but that is not an epidemic. That is cohort replacement.
I realize this is subtle, and its importance is probably lost on many readers. But believe me when I say for anyone literate in population health science, it stands out as a far larger error in the use of the term than the simple fact that vaping is not a disease, or even the “looking at only one line in the ledger” game.
To summarize how I believe we should respond to these innumerate “epidemic” claims: First, we should push back against the use of the word to refer to a behavior rather than a disease. This is not, however, because of some naive language purity urge, a failure to recognize that words get used metaphorically. Rather, it is because this usage is part of tobacco controllers’ game of trying to define the behavior as a disease. They are not actually trying to expand the definition of “epidemic” here, but that of “disease”, and we should push back.
Second, the strongest substantive replies are as follows: The FDA version of the claim is based on carving out one particular product, which is taking away market share from other products (which, oh by the way, are a hundred times worse for you). Always go back to the entire category, and perhaps consider noting the analogy of “Marlboros manufactured in 2018”, whose usage is up by infinity percent. As for the WHO version of the claim, it is simply factually false.
Third, the FDA version of the claim is actually something worse than false: it is nonsense. It is one thing to say something that could be true but happens to be false. It is another to utter a string of words that simply make no sense. There cannot be an epidemic of anything among 17-year-olds, based on year-to-year comparisons, because these are entirely disjoint populations. Again, you may have to take my word for it, but this is actually the clearest misuse of the word in this entire embarrassing mess. The supposed health scientists at FDA should understand this, though I expect they do not understand and are clearly immune to embarrassment.