# Intention to Treat

When my son was three, we enrolled him in a study of a vision condition that runs in my family.  They wanted us to put an eyepatch on him for part of each day, with a little sensor object that went under the patch and detected body heat to record when we were doing it.  They paid for his first pair of glasses and all the eye doctor visits to check up on how he was coming along, plus every time we brought him in we got fifty bucks in Amazon gift credit.

  
I reiterate, he was three.  (To begin with.  His fourth birthday occurred while the study was still ongoing.)

  
So he managed to lose or destroy more than half a dozen pairs of glasses and we had to start buying them in batches to minimize glasses-less time while waiting for each new Zenni delivery.  (The patching protocol was useless without the glasses to go with it.)  He would sneak his eyepatch off when we weren't looking and rely on having more parents than the average bear, most of which parents have ADHD diagnoses, to confuse us about whether he was supposed to be patched at any given time.  The sensor doodad and its backup were lost or "lost" in the couch cushions over and over until we couldn't find either one again.  He was at first extremely prone to falling asleep once the patch was on, which meant he wasn't looking at things with his uncovered eye during the intended patch time.  We bribed him with a dollar per day he was cooperative with the patch (an amendment from our original plan to just give him the value of the Amazon credit - between the replacement glasses and the bribery we were down on net.  The bribery alone would have ensured that if he'd been more cooperative, but he wasn't.)

  
They didn't drop us out of the study.  In fact, they eventually concluded that their protocol had had the effect they wanted - he's apparently trained away the asymmetry that made it impossible for my father to use a binocular microscope in med school.  They didn't make a fuss about the missing sensors, the forgotten days, the napped-through patching hours, the lacunae in glasses compliance.

  
He was three.  They knew he was three.  No human three year old is perfectly compliant with a patch protocol and the process of trying to force it to occur perfectly would be nightmarish for within the study, let alone if they popularize this approach as a clinical recommendation for everybody whose kid presents with the same problem.  They were running the study on [*intention to treat*](https://en.wikipedia.org/wiki/Intention-to-treat_analysis).  
 

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Maybe real communism has never been tried, but from an intention-to-treat perspective it performs dreadfully.  Condoms work ninety-eight percent of the time - wait, no, scratch that, in intention-to-treat terms it's more like 87%.  Is Duolingo better than a textbook?  Turns out the biggest term in this estimate is how likely I am to actually pick each one up after having decided I should, and it's not close.

  
You know how "people will not just"?  This is the science term for "people will not just".  If you have a plan, your plan needs to be efficacious enough to work after attrition in the population of those who make vague noises about trying it; robust to the chance that it actively harms some subset of those people and they drop out of your project; capable of surviving normal long-run levels of human error, either by way of juke tolerance or systems built in to steer everybody toward checklists and no-fault postmortems.

  
I think this is useful to have in mind when discussing any protocol which might contact humans or other chaotic systems eventually.