“We’re going to estimate treatment effects via an ancient rock-throwing technique.”
We developmentistas often associate randomized impact evaluations solely with development interventions (I’m looking at you Eva Vivalt), so it’s easy to forget that there are other researchers out there doing some really bizarre RCTs. For example, did you know that randomzing paracetamol is still a thing? Psychologists seem to think that it augments an individual’s emotions, in addition to the palliative effect it has on pain. In a recent Psychological Science article, several researchers wanted to observe whether paracetamol blunted our emotional responses to distressing events.
The first experiment they ran was, well, moderately distressing. There were two types of treatment: some participants were asked to write about a `placebo subject’ – something innocuous, where the treatment group was asked to write about their own death (distress! distress!). This was cross-cut with a standard double-blind randomization of paracetamol. Then the researchers recorded their outcome of interest, which was a bit….odd:
Finally, participants read a hypothetical arrest report about a prostitute and were asked to set the amount of the bail (on a scale from $0 to $999). This measure has been used in a number of other meaning-threat studies (Proulx & Heine, 2008; Proulx et al., 2010; Randles et al., 2011; Rosenblatt, Greenberg, Solomon, Pyszczynski, & Lyon, 1989). Participants are expected to increase the bond amount after experiencing a threat, because trading sex for money is both at odds with commonly held cultural views of relationships and against the law. Increasing the bond assessment provides participants an opportunity to affirm their belief that prostitution is wrong.
Um, I think we’ll probably leave that out of our next household survey, but fine. What was the result? The average bond levels set by each treatment group was similar, except for the group which received a distressing event but not paracetamol.
The researchers claim this means that acetaminophen (paracetamol) is actually blunting people’s normal response to the emotionally-distressing task (i.e. punishing prostitutes). In the difference between the control placebo and the `mortality salience’ placebo – approximately $120 dollars more, but there appears to be no significant difference between the treatment and control groups who were not given the drug.
Now things get even a little more bizarre. The researchers want to replicate the experiment with a similar premise but a different outcome measure and a different distressing activity. So this time they made the control group watch a four minute clip of The Simpsons, where the treatment group had to watch four minutes of the David Lynch short film “Rabbits”, which is composed of creepy humanoid rabbits You can watch the entire thing here. I recommend having something lined up to cheer you up afterwards.
In this case the respondents had to choose how much to fine a group of public rioters. The results were very similar to the first experiment: the treatment group which did not receive any paracetamol ended up fining the rioters substantially more, but there was little difference between the other three groups. Again the researchers argue that the paracetamol made the difference.
Before you start slipping people paracetamol before you give them bad news, there’s a number of reasons we might be very wary of these results. First, the theoretical groundwork is a bit shaky – while there are some psychology experiments that paracetamol does influence what they call “social pain,” there is no compelling physiological link, other than some inconclusive evidence cited at the beginning of the article. We should discount results more heavily when they don’t have such a strong grounding in either theory or prior evidence. We certainly shouldn’t use them for anything as headline-grabbing as “What is Tylenol Doing to Our Minds?”
The results also rely on what the psychologists call a meaning-maintenance model which predicts that individuals will seek compensatory affirmations of their beliefs when their expectations or `meanings’ are threatened by outside stimuli. Thus, punishing a prostitute or a rioter – the authors argue – gives the respondent a chance to affirm their belief that these practices are wrong. I don’t know enough about the subject to say whether or not the meaning-maintenance model is a sensible way of describing human behaviour, but the result seems dependent on a few too many assumptions: A) that paracetamol interacts with a part of the brain that generates these compensatory desires B) that the treatments in this experiment themselves would generate compensatory desires and C) that the outcomes of these experiment are meaningfully measuring this desire to assert one’s beliefs after a distressing event.
That said – this is why we do replications, and the researchers do well to set up two separate experiments. Plus they got to randomize David Lynch. This is awesome.