Science Lesson: on “anecdotes”

by Carl V Phillips

Following a twitter conversation between some vapers and some others who mistakenly think they understand science, I decided to write a quick lesson for those who might want more than a bumper-sticker about this. The issue at hand is whether you can learn anything about the world from individual testimonials about people’s experiences or other one-off “anecdotes”. The answer is obviously yes. It is safe to say that more than 99% of what each of us knows comes from such evidence. So why do so many people not understand this obvious fact, and habitually denigrate such evidence as “anecdotes”? It seems to be because they are stuck in a grade-school understanding of science.

I have written entire papers that are substantially about this point, but here is my quick explanation for how to better think about this. (Oh, and as an aside,  anyone who thinks that this exposition is more correct due to the fact that I have also published versions in journals knows even less about understanding scientific evidence, but that is another story that readers will know I cover elsewhere.)

A good basic lesson in science for a seven-year-old is the following: Just because one reasonably likely event followed another reasonably likely event does not mean that the first caused the second. We all know that intuitively in most cases, but it is also easy to get tricked under particular circumstances. This is basically what superstition is — institutionalizing such unfounded observations in a desperate search for explanations for “random” events. Moreover we can be intentionally tricked into believing otherwise by people who profit from the claim of cause and effect. The most notable example is the medical profession, whose leading method throughout time (and to a substantial extent still today) was to wave their hands over someone and then take credit for the recovery that was going to happen anyway.

Moving on to about age eleven, with a bit of math available, another useful lesson is that unlikely events happen and seeking an explanation for any one of them is likely to result in the formation of superstition. My favorite example is starting a lesson with: “wow, you would never believe what happened! I was walking to class and saw a car with license plate number B2X 113…” (or whatever would fit the pattern for local license plates) “…What is the chance of that happening?! I wonder what caused it?” Of course, the chance of that exact event happening is impressively small. But the chance of seeing a car with some license plate number is about 100%, and since you could tell that story no matter what the number is, there is nothing interesting here.

With those lessons, we immunized grade-schoolers against being tricked by coincidence, teaching them to not over-conclude from one observation. We also teach young children “do not get into a car with a stranger”, which is good simple advice at the appropriate level for them. It guards against the worst possible mistake. But anyone who does not eventually learn that life is not so simplistic will have a rather hard time getting from the airport to their hotel.

Unfortunately, far too many people only get to the grade-school level in their understanding of scientific inference, but nevertheless think they are experts. People working in serious sciences get past that and learn the value of single observations (imagine: “The orbit of Mercury is not what Newtonian physics predicts. But who cares? That is just one anecdote. Ignore it.”). But a large portion of those pontificating about health science, particularly physicians, do not understand scientific inference any better than fifth grader. The worst problem is that they do not realize that.

Learning exactly how to tease the informational nuances out of any data, whether it be columns of numbers or a single personal testimonial, requires a lifetime of study and some decent intuition. But it is possible to teach a simple lesson to the “that is just an anecdote!!” crowd to make it obvious that their “never get in a car with a stranger”-level understanding is overly simplistic.

Consider a man who at 3:00 has no major injuries; shortly thereafter he gets into a car crash (and nothing else noteworthy occurs); upon talking to first-responders at 4:00 he say “I am basically ok, but I really hurt my wrist in the crash”; at 6:00 that evening, an x-ray shows he has a broken wrist. He tells us this anecdote, leading with the causal claim, “I broke my wrist in that car crash.” Do we believe his assertion of cause an effect? And, thus also conclude that (sometimes) car crashes cause broken wrists? It was, after all, just one story.

Of course we believe him. We are not idiots.

Would we say “I am only going to believe that car crashes can cause broken wrists after I see a statistical study in a journal that shows that to be the case”? Again, no, because we are not idiots.

I figure it is a safe bet that no one has ever done that study, comparing the hourly incidence rate of wrist fracture proximate to car crashes to the rate among those not experiencing car crashes. Again, because no one with the basic literacy skills to conduct a study is that much of an idiot (though if they did, they could undoubtedly get it published in a peer-reviewed journal). Now if the question were how often do car crashes cause wrist fractures, that would require gathering statistics, and that has been done. But it is obviously not necessary for assessing the basic point of whether the phenomenon ever happens. Moreover, the nice clean, controlled, artificial experiment with crash test dummies would tell us even less about the basic question of whether this phenomenon actually ever happens in the real world.

The only thing that would cause us to seriously doubt his claim is if we somehow thought he was lying about the events. Otherwise, if those events happened, we have evidence of cause-and-effect as convincing as ever exists in the real world. There is never any actual technical proof of causation in the real world, but this is evidence at the level that we loosely call proof. Sure, it is theoretically possible that hidden space aliens shot his wrist with a ray gun at just about the same time as the crash, or perhaps listening to Aerosmith on the car radio caused his wrist to fail (this is why there is never any proof), but it seems safe to assume otherwise.

So what is the difference between this “anecdote”, in terms of providing scientific evidence, and the grade-school teaching example (say “he had a cough; he took some homeopathic medicine; the cough went away; therefore the medicine cured the cough”)? There are a few key features, and recognizing them is the difference between thinking like a scientist and just repeating imperfect rules-of-thumb you learned in grade school. First, there are good reasons to believe that a car crash could cause a broken wrist, unlike singing along with Walk This Way. I trust I do not have to explain those. Second, the incidence rate of spontaneous wrist fracture, unassociated with any dramatic event, is trivially small during any given afternoon, in contrast with the rate of an extant cough going away sometime over a several-day period. Thus it is safe to rule out the “it would have happened anyway” alternative. Third, the event and the outcome are both well-defined and definitively occurred, unlike many superstitious cause-and-effect claims (e.g., “I prayed yesterday that I would have a good day today, and, sure enough, I found $100 in the sofa cushion” — something similar to the license plate example).

Of course, these are not the only characteristics that might cause you to draw scientific conclusions from a single observation. (They do not describe that case of drawing conclusions from Mercury’s orbit, for example.) There are no simplistic rules like that, which is why scientific inference requires thinking, not recipes. But they are the useful ones in this case.

In what other case might these observations about drawing a conclusion from a single observation be useful? Obviously the case of people quitting smoking thanks to e-cigarettes or some other low-risk substitute. There are obvious good reasons to believe that finding a better substitute for a behavior can cause an end to that behavior. The rate of spontaneous, unexplained smoking cessation in a given week, or even month, is very small. The ostensible cause and effect are very clearly defined and definitively observable. Thus, when a single individual says “I smoked for years; I tried to quit some times but failed; but then I tried switching to e-cigarettes and that finally let me quit smoking”, you either have to claim she is lying about the basic facts or recognize that it is as close to proof as can exist that e-cigarettes caused her to quit smoking. From that you can further conclude that — at least sometimes — e-cigarettes cause smoking cessation. No further study is necessary. Of course, if you want to figure out how many times this has happened or how often the attempted switch is successful, then you need to gather the right statistics; but those are different questions.

So, dear reader, congratulations. If you read this and understood it (or already understood the points, of course), you understand science at better than the “never get in a car with a stranger” level. It is not, by itself, everything you need to know about drawing scientific inference from non-systematic observations, but it is a definite step up from the naive, simplistic, and grossly incorrect claims that “anecdotes cannot prove anything” or “anecdotes are the lowest form of evidence” (whatever that means).


10 responses to “Science Lesson: on “anecdotes”

  1. That was an absolute pleasure to read after the twaddle this blog is referring to. Thank you.

  2. Carl V Phillips

    I will add (here — I was trying to keep the post shorter than it ended up being) my other favorite example of how a single observation can provide overwhelming evidence:

    You walk into a room for the first time. There are a lot of switches on the wall (think classroom or conference room). You flip the first one you reach and the lights come on. You conclude that flipping that switch causes the lights to come on. You have one observation. But you are absolutely sure of the causal conclusion. You file it away and remember it in the future for when you come into the room, without the slightest hesitation or doubt. Why? (hint: it is pretty similar to the reasons for the more complicated car crash example)

    Now if the question were “of all the switches in the room, which ones affect the lights?”, you would need to do some more research before you were sure. But you did not really care about that — you have a way to turn on the lights and that is all you wanted.

    Now, to add a new wrinkle, if someone offered you $1000 to tell them how to turn on the lights (and you have to get it right on the first try), you might be inclined to flip that switch off and on a few more times, just to be sure. Why? Because it is so utterly trivial to perform that experiment (and, yes, this is an example of that ever-preferred experimental research design) that even though you are already 99% sure, it is worth becoming even more sure. But imagine that instead of getting that offer while standing next to the switch you got it after you already got home. Would you drive back to the venue in order to flip the switch (let’s assume you are absolutely confident of your memory)? Probably not, because further testing when you are already 99% sure is simply not worth the much higher cost of doing that research.

    By that token, imagine if there were some massively costly downside to falsely believing, as rational people do, that for most (a few errors will inevitably exist) of the people who testify that they quit smoking due to e-cigarettes, that is really true. In that case we might want to put this to some kind of more severe test, paying the very high price for that (e.g., banning e-cigarettes to see if vapers really started smoking again). But since the rational level of confidence in our conclusion is very high (well over 99%), and the downside of that being an error (a bunch of people enjoying vaping rather than being abstinent) is so low, it would be insane to do that research.

  3. Thank you. It tickled my funny rist bone, that I broke last summer after having my bicycle that comes a part in two pieces repaired at a local hardware store, come a part in two pieces while I was on it, going 10 mph. OUCH! I was scientifically about age 2, immediately after, when I started cursing in pig latin (bs) in loud English! An anecdote that so appreciates all you do for Science and for Consumer Activists for SafER Alternatives Association.

  4. Carl V Phillips

    By the way, the two self-described scientists that were talking nonsense in the twitter thread that inspired this, David Gorski ‏@gorskon and “Cathal” ‏@penj3, were both explicitly invited to respond to this analysis if they thought it was wrong. Neither did so. That is also a very useful form of scientific evidence: When those who want to insist that I am wrong cannot come up with anything to say that supports their desired claim, it is good evidence that I am right.

  5. I absolutely must come back and read your blog more often! Very insightful, and outright useful.

    Thank you sir!

  6. Thank you Carl, nicely explained, I’ve lost count of the number of times I’ve heard the statement, “anecdotes are not evidence”, when quite clearly they are indeed evidence. Its insulting to constantly be told by those in “tobacco control” or their followers, that I am lying or my story is of no importance, when I explain how the day I started vaping, is the day I stopped smoking tobacco, after being a smoker for more than 20 years. Vapers everywhere come up against this same argument, to the point where literally millions of ex-smokers world wide have quit smoking tobacco using vapourisers, but public health officials continue to ignore this vast body of evidence in favour of their own unsupported beliefs and theories. (I guess many of those in public health, and tobacco control in particular, have not progressed beyond their primary school level of scientific understanding).

    Anyway, I know that you already understand what is happening in regards to vaping, and “tobacco control”, so I wont go on. Their problem with vaping is nothing to do with either health or science, it has always been about money and control. They use their rudimentary understanding of science as a weapon against vapers, rather than as a tool for better understanding, and gathering knowledge.

  7. The main problem with folks repeatedly using pseudoscience and utter rubbish to ‘persuade’ legislators (many of whom are later too embarrassed to admit they were had) is that there is no downside.

    Were it the case there was a penalty to be paid for submitting data that failed the litmus test of the real world then this would at least be a selective pressure on nonsense…and would certainly evoke a rethink before offering BS!

    I would include all parties in that suggestion…. The ANTZ, vapers, legislators, politicians, health officials, companies….everyone. I’d also consider anyone having a problem with it to be fearful of the outcome…and tacit acceptance that they know their money cannot follow their mouth!

    • Carl V Phillips

      I agree that there is very little downside to lying to unsophisticated lawmakers, and that is relevant especially to local health boards and city councils who are clueless and do not have the resource capacity to get a clue, but make laws anyway. This is why lying is the common practice. There is pretty close to no downside to lying at the state level either. At the federal legislive level it gets a bit dicey because sometimes they call people in for hearings and they have enough staff capacity to acquire some real expertise (assuming there are legislators who oppose the liars’ agenda) and therefore ask good questions. But when we are talking about executive branch actors, there is a lot more recourse when they are working from lies. They are answerable, as opposed to legislative actors who are empowered to do whatever they want for whatever reason they want.

      Also, of course, it is up to us to create some cost from lying in every case.

      I strongly disagree with the “everyone does it” claim. This is the standard false equivalence practiced by the corporate media, wherein they have no expertise on what they are writing about, or deliberately refuse to exercise any judgment, and thus turn everything into a he-said-she-said sporting match (they know how to report on sports — not so much anything else). Even when one side is based entirely in blatant lies, they try to falsely portray it as “everyone” by finding some debated claim by the other side (often one that is actually true, but just that someone has claimed is false, and/or something not actually critical to their case) and suggesting that is the same. That describes the anti-THR situation.

      The ANTZ *entire* case is based on lies. Their leading spokespeople aggressively and deliberately lie. That is complete different from the pro-THR side. Yes, there are random consumers and vendors who say things that are not supportable or are out-and-out false. But that is inevitable when there is a lot of random chatter. Even many of the supposed experts make false claims (e.g., a favorite claim right now is that there cannot be a gateway effect from ecigs because smoking prevalence is dropping; this is clearly false). But the most serious and expert voices for THR are impeccably honest, in contrast with the leading anti-THR voices. More important, the case does not depend on any of the false claims. They are out there, but they are not foundational. This contrasts with the anti-THR side, whose entire “argument” is based on falsehoods.

  8. Pingback: What Do We Know? - Facts Do (Don't) Matter

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