How to Kill a Zombie Idea

Halloween approaches, and there are zombies everywhere. I’m wondering: How do you kill a zombie? Is it even possible to kill a zombie? After all, they are already dead. They get shot full of holes, but they clamber back to their feet and continue to shamble along. Chop off a limb? No big deal. They keep coming.

The Problem of Zombie Ideas

You might think I would be safe hiding in my office at the university, but not really. The zombies surround me. Anywhere I look in my office, I can find zombies. These zombies aren’t stumbling along trying to grab me. These zombies are ideas. They are in the textbooks on my shelves: Wrong ideas and theories with piles of disconfirming evidence. Effects that one set of researchers found but that no one else can replicate. These are zombie ideas. And like the other zombies, they want to eat people’s brains.

Like other zombies, these zombie ideas refuse to die. Scientists shoot evidence at these zombies. The theories are full of holes, but they keep showing up in our textbooks. They keep appearing in the minds of our students. They continue their undead lives in public awareness.

The problem of zombie ideas is widespread. They seem to be wandering through every academic domain—Undead, unkillable and spreading bad ideas. Paul Krugman, the Nobel-winning economist, has written an entire book on zombie ideas in economics and politics. He’s concerned with zombie ideas that guide decision-making in political contexts–ideas such as cutting taxes on the wealthy leads to economic growth and trickle-down benefits. As Krugman has written in his book and at the NY Times, the evidence does not support the claims about tax cuts. It is time for that idea to die. And yet, that zombie continues to shamble along and leads to more policy advice.

Zombie Ideas in Psychology

Most academic fields have zombies running through their textbooks. Simmons, Nelson, and Simonsohn (2011) noted that psychology suffers from a problem of false positives. These are findings that are reported once–but that are probably not reliable findings. Nonetheless, those false findings are remarkably persistent. Other researchers try to replicate the result and fail. Sometimes there are multiple failures to replicate the finding.

Each replication is like firing a bullet at a zombie. The zombie is riddled with bullet holes but keeps walking along. The scientific finding is riddled with holes from the failed replications. But it keeps showing up in textbooks. And the zombie idea infects the brains of another generation of students.

A Zombie Idea Example

Let me give one example of a zombie idea: Ego depletion. This was an attractive idea, at least at the start. Roy Baumeister and colleagues (1998) first proposed this idea and provided some supporting evidence. The idea is simple: making decisions and engaging in self-control uses a single internal and limited resource. Think of it as something like will. If you have exerted that type of effort for a while, you may have depleted your ego. If you’re required to engage in another task that requires some of that limited resource, you may give up sooner. It is a very attractive notion. Maybe it feels right to you.

I love some of the original studies on ego depletion. Baumeister and colleagues had people eat radishes or cookies first. Eating the radishes was apparently harder work. Those who ate radishes gave up more quickly on the next task, which involved solving impossible puzzles. They had supposedly depleted their ego, their limited resource.

But other psychologists have often found these effects challenging to replicate. Several different researchers have tried to replicate this zombie effect (Hagger et al. 2016; Vohs et al., 2021). But the effect is elusive at best. Actually, I suspect it is a zombie. The problem is this zombie continues to show up in textbooks.

How Science Tries to Kill Zombies

I don’t want to pick on this single effect. I could describe several other ideas and attractive theories and where there were initial findings that seemed supportive. But over time, the effects haven’t held up. Learning styles, flashbulb memories, and repression come to mind.

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Supposedly, science is self-correcting. Someone publishes a set of findings and makes a theoretical claim. Other researchers test those ideas. If they can’t replicate or they find flaws, we set those ideas and theories aside. And science does work this way, mostly.

But sometimes, attractive ideas can turn into zombies. The ideas, claims, findings, and theories have long lives after they are dead. Shambling along in textbooks and the minds of our students.

So how do you kill a zombie idea in science? I’m not completely sure. Evidence is supposed to be the magic bullet, the silver bullet, the wooden stake. But many zombie ideas in psychological science and elsewhere seem remarkably resistant to evidence. The open science movement is finally trying to provide more consistent evidence to kill some of these zombie ideas.