The Ebola Formula

Perhaps the study of law has something to add to the study of medicine, at least in one context.  A few weeks ago, I was talking with my brother and sister-in-law about their decision to invest a sizable chunk o’ change on their boys learning to “swim” when they were about eight months old.  These lessons are designed to ensure that if the boy falls into a pool, even fully clothed, he can quickly roll onto his back and float and cry until rescued.  The iterative training takes place over a several-week period and scares the hell out of the kid at the beginning. It is done under very strict conditions and almost always results in the kid learning how to stay alive for several critical minutes should the unthinkable happen.

So my sister-in-law is telling me about a conversation she had with one of her friends who criticized her for putting her sons through this training because of the “trauma” and the little bit of water the kids occasionally ingest during the training that some sometimes hurts their “wittle tummies.”  Her friend vowed never to subject her children to such cruelty.

“The BPL on that one is easy,” I said.  “No question that you were right and your friend was wrong.”

“BPL?” she quite reasonably asked.

“Why yes, BPL,” I responded.  “It is life’s most important formula.  It works for swimming training just as well as it works for Ebola.”  Knowing I was being coy – I like to yank her chain from time to time – I finally explained:

This is a simple formula I teach my students in Torts as they learn to analyze whether an individual acted negligently in any given situation.  P equals the probability of harm and L equals the gravity of harm risked by the conduct in question. (No one really knows why L was chosen instead of G for this formula – probably something to do with Latin).  When multiplied together, they give you the magnitude of risk posed by a given activity.  B equals the burden of avoiding the risk.  If B is less than P multiplied by L (B<PL), then the rational (reasonable) decision is to engage in the activity.

To illustrate, look at the choice faced in deciding whether to get the swimming lessons.  The first task is to define the activity to be evaluated – Should the parents give their kids these swimming lessons?  Set P as the probability of the kid falling into a body of water when momentarily unsupervised, and L as the gravity of harm if this happens.  The probability of the kid falling into water is pretty low – say 1/100 of 1%.  But the gravity of harm that would be suffered is quite high – death or serious injury.  So while the probability of harm is low, the gravity is astronomical.  The burden to be evaluated is the activity necessary to avoid the risk — the fleeting fear and tummy trouble junior suffers, plus the cost (financial, emotional, and inconvenience) associated with the lessons.

When measured against the relatively minor burden of putting junior through the lessons and paying the cost, the results should be clear for most people: B<PL.  In other words, the magnitude of the risk outweighs the burden associated with avoiding it.  Accordingly, the rational decision would be to give the kid the lessons.

Whether we acknowledge it or not, we make BPL decisions during most moments we are awake.  We are constantly weighing costs and benefits in what we eat, what we buy, what time we go to bed, etc.

The recent measles outbreak has sparked a debate that will only increase in volume and intensity over the next few years as such outbreaks increase in size and scope. Why?  Because too many parents reached different BPL decisions than others.  The way to keep diseases such as measles at bay is to inoculate the entire herd – that way no one gets it or spreads it.  But several years ago, many parents looked around and decided that since all the other kids in the herd were getting inoculated, then they didn’t need to inoculate their kids.  After all, if the other kids in the herd don’t catch measles because they are inoculated, then their kids can’t catch it even though they aren’t inoculated because the disease isn’t in the herd.

Here is the BPL equation by the parents.  First, identify the question being evaluated – Should I get junior vaccinated against the measles?  The probability of getting measles is really low because the entire herd is getting inoculated (and has been for years) so there will be no one to infect their kids with measles.  And while the gravity of harm associated with measles is potentially somewhat severe, it isn’t life-threating for most of those infected.  Thus, the magnitude of risk associated with contracting measles (probability multiplied by gravity) is relatively low, or so the parents believed.  On the other side of the equation is the burden encountered to avoid the risk – getting the inoculation.  Most parents considered this to be very low – getting junior jabbed with a needle just after his first birthday is little more than an afterthought.  The kid cries for thirty seconds, but the kid cries every hour or two anyway – no big deal.  So most parents had their kids vaccinated because the minor burden is less than the moderate risk – B<PL.

But we are now finding out that the “sophisticated” parents (usually wealthy & highly educated) saw the equation a bit differently.  Like most parents, they concluded that since the other parents were vaccinating their kids, the probability of junior getting measles was very low because there would be no other kids with measles to spread the disease.  Thus, they reasoned, the magnitude of risk (PL) approached zero.  But, and this is critical, these parents read or heard about a study that suggested autism and other similar conditions might be traced to these vaccinations, so the burden of avoiding the risk (B) was actually higher than the momentary hissy fit junior would pitch after getting jabbed.  So much higher, they reasoned, that now the burden outweighed the risk (B>PL), so they found it rational not to inoculate junior.  (Incidentally, the study these parents relied upon was quite heavily criticized and controverted when it was issued, and later thoroughly discredited, withdrawn, and labeled as “an elaborate fraud”).

As a direct consequence, we get a measles outbreak, at the happiest place on earth (Disneyland), no less.  Why?  Because the parents many call “savvy” or “clever” (others call “selfish”) were larger in number than the “savvy” parents supposed when they made the decision – it turns out quite a few other members of the herd weren’t inoculated either.  So when one of them contracted measles, it spread quickly throughout the herd.  In fact, the vaccination rate in some wealthy areas of Southern California is now as low as impoverished and war-torn South Sudan.  I suspect this will change, however, in the wake of this outbreak because most people act rationally, and when armed with the actual (rather than supposed) information that informs a BPL analysis, they will make more rational choices.

This highlights an important point – a correct BPL analysis requires accurate data points.  It is simply an empirical question.  Which brings me to Ebola.

The same formula must be applied to the ongoing, though thankfully diminishing, discussion about how to handle people coming from locations where they were potentially exposed to Ebola.  It was as disappointing as it was unsurprising that the majority of Republican politicians accused the Obama Administration of playing politics with Ebola, while the majority of Democrat politicians were accusing Republicans of doing the same thing.  One side argued that anyone coming from an infected region should be quarantined for twenty-one days, while the other argued that doing so amounted to unnecessary scare tactics and would hamper the work on the ground in Africa because fewer people would be willing to go and help stop the spread of the disease at its source if they were thereafter quarantined.

So here is the question – Should we quarantine people, even if they don’t currently have a fever (and are thus potentially contagious), for twenty-one days after they return from an infected area?  At bottom, this isn’t a political question, but an empirical one.  The only rational approach to this conundrum is to apply the BPL formula.

Is the probability of harm (virus spreading in the United States) multiplied by the gravity of this harm (mass death and suffering) outweighed by the burden encountered by holding people in quarantine for twenty-one days?  In order to answer that question, one needs to assign values to the variables.  We can all agree that gravity of harm is quite high if Ebola were to break out in the United States.  Thus, L is HUGE.

The more important question is what is the probability of the virus spreading associated with allowing one who has come into contact with those infected by the virus, but isn’t currently running a fever, to roam freely in his or her community?  Relatedly, how big is the burden of confining those who have been exposed until we are confident that person isn’t a threat to the community?  This, of course, includes the financial and personal burdens placed upon those paying for the confinement and on those who have to be confined.  It also includes the deterrent effect that such confinement would have on medical professionals who might be willing to go to Sierra Leone, etc., for four to eight weeks if they could go straight home (assuming they had no fever), but wouldn’t go at all if they had to be confined for three weeks thereafter.

This question was brought into sharp relief when nurse Kaci Hickox resisted being quarantined after returning from West Africa.  She received roughly equal parts praise for asserting her “civil rights” and scorn for “selfishly putting others at potential risk.”  But who was right?

Once again, this should be an empirical and scientific question, and not a political one.  While I am not at all an expert on Ebola, I can read.  Experts tell us that for those infected, on average, there is a sudden onset of flu-like symptoms 12.7 days after exposure.  But it is also apparently true that for 4.1 percent of patients, their symptoms will emerge more than 21 days after exposure.  And according to the New England Journal of medicine, approximately 13 percent of those infected never ran a fever.  So how does this affect the application of the BPL formula?

As noted above, the gravity of harm is quite high if Ebola were to spread in the United States.  But what is the probability of it spreading if we don’t quarantine for 21 days those who come back from an infected region?  It is probably fairly low, but far from non-existent.  In order to virtually eliminate the risk, it appears that they would need to be quarantined for something like 30 days because 1 in 25 won’t show symptoms (and thus be presumptively contagious) until after the initial 21-day period.  Likewise, the solution can’t be simply to quarantine those running a fever because 1 in 8 apparently won’t even run a fever when they are contagious.

And how big is the burden that would be encountered by quarantining for 21 days (or 30) all who go to West Africa to assist in containing the outbreak?  The financial cost is not significant, at least when weighed against the risks.  But the deterrent effect is likely quite significant – convincing a doctor or nurse to spend a month or three in West Africa is pretty tough.  Adding another month in relative isolation after the return raises the burden even higher.

So what is the solution?  It is simple – put some really smart and informed (and apolitical) scientists/doctors/nurses in a room and have them apply the BPL formula.  Whatever they decide, we accept.

Just one guy’s opinion, but remember that all of life is a BPL.