As rationalists, we are trained to maintain constant vigilance against common errors in our own thinking.  Still, we must be especially careful of biases that are unusually common amongst our kind.

Consider the following scenario: Frodo Baggins is buying pants.  Which of these is he most likely to buy:

(a) 32/30

(b) 48/32

(c) 30/20

If you're like me, your answer is (c).  Frodo, as we know, is about 4' tall, so his inseam is much more likely 20'' than 30''.

But like me, you'd be wrong.  Since there aren't *actually* any hobbits, all we know is that we're talking about a person named Frodo Baggins, who is male.  And the most common pants size is 32/30, so the correct answer, given our actual state of knowledge about the real world, is (a).

This is what researchers call Fictional Bias, and there is evidence that it affects virtually every domain of decision-making.  The mistake is using information from fictional sources in real contexts.  It is the more-pernicious cousin of generalizing from fictional evidence - instead of merely generalizing, we treat real objects and persons as though they are the specific fictional entities they resemble.

We're of course familiar with particularly egregious examples of people confusing fiction with reality.  For example in the 1930's, there were multiple cases where someone was killed for having the same name as the serial killer of children from the movie M.  But these could be written off as merely disturbed individuals.  But as it turns out, we're affected by this bias in our daily lives.

Examples abound in the literature, though the name "fictional bias" is not always used.  A 1984 study by Dr. Sidney Zweibel and Dr. Emilio Lizardo asked subjects to trust someone with an unusual name.  Subjects were 70% less likely to trust when the person had the same name as a fictional villain.  A 1989 study by Dr. Wayne Szalinski established that subjects were 89% more likely to agree to take an experimental drug, when it was named after a fictional drug (for example Ephemerol).

The moral?  It stands to reason that we need to be careful where our intuitive inferences come from.  For a group that consumes so much science fiction and fantasy, we must be especially on our guard.  (Also, this post was an April Fools prank; the effect may or may not be real, and all citations are either irrelevant or fictional.)  It might even behoove us to discourage the reading of fiction amongst aspiring rationalists.

Kahneman, D. and Frederick, S. 2002. Representativeness revisited: Attribute substitution in intuitive judgment. Pp 49-81 in Gilovich, T., Griffin, D. and Kahneman, D., eds. Heuristics and Biases: The Psychology of Intuitive Judgment. Cambridge University Press, Cambridge.

Szalinski, W. 1989.  Recollection of fictional medication. Journal of Cognitive Minification, 67: 173-186.

Tversky, A. and Kahneman, D. 1982. Judgments of and by representativeness. Pp 84-98 in Kahneman, D., Slovic, P., and Tversky, A., eds. Judgment under uncertainty: Heuristics and biases. New York: Cambridge University Press.

Tversky, A. and Kahneman, D. 1983. Extensional versus intuitive reasoning: The conjunction fallacy in probability judgment. Psychological Review90: 293-315.

Zweibel, S. and Lizardo, E. 1985. Fictional bias in interpersonal trust.  Cross-Dimensional Neurosurgery, 45: 307-324.

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The initial example is inane. I believe XKCD has an appropriate comment on the matter.

In more detail: While strictly speaking "Frodo Baggins" may not be a unique identifier, there is a fictional person people will understand it to mean without additional context; as such, without that additional context, it must be taken as the usual meaning of "Frodo Baggins". Hence we get it "wrong" only because you used the name "Frodo Baggins" with a meaning other than its usual one. (Analogous to the comic.)

If you did something to indicate that it need not be the usual Frodo Baggins -- for instance, opening it with "Someone named Frodo Baggins", and the effect still (or rather actually) occurred, that would be an example.

Edit: Oh, hell. Just took a look at the references. I had actually thought this was intended seriously...

It's a standard conversational shorthand to just say "Frodo Baggins" instead of "Frodo Baggins from the Lord of the Rings". Going "ha ha! I didn't really mean THAT Frodo!" is a sophomoric word game, and completely unrelated to the topic of fictional evidence.

I agree with your point, but all you really do is describe the idea. links to two other posts on this topic already, one of which is part of the Sequences, and this post doesn't really seem to add anything new.

You might find some of Gerd Gigerenzer's work interesting (just google his name, he has a lot of it online). He has a similar opinion of many of the classic experiments in heuristics and biases.


I really, really dislike April Fool's jokes like this. Somebody will stumble onto this post at a later date, read it quickly, and come away misinformed.

I'll grant that the obviously horrible "Frodo Baggins" example should leave a bad taste in rationalists' mouths, but a glance at the comments shows that several readers initially took the post seriously, even on April 1st.

I agree completely. If you didn't read the references or notice the date, the article seems completely legitimate. It makes a couple weird claims (fictional drugs?), but if you didn't know the literature they wouldn't necessarily seem any stranger than the actual things people do (like anchoring their estimate of a car's value to their social security number). Remember that the absurdity heuristic is not a very good mode of reasoning!

So this means that while people who know Less Wrong can have a little inside joke, people who are new to rationalism and behavioral sciences could easily be fooled.

but if you didn't know the literature they wouldn't necessarily seem any stranger than the actual things people do (like anchoring their estimate of a car's value to their social security number)

Funny you should mention that. When I first had the idea for this post back in January or February, I specifically wanted to think up a fictional bias where the examples would be stranger than anchoring, and about as relevant to everyday life if true. I could not think of one. I finally ended up writing this at the last minute when I realized "fictional bias" was a pun and decided to write the post around that title.

What I'd really like to know, is whether anyone saw my tweets or facebook posts about trying to think up a nonexistent bias, and was still fooled by the post.

The post's own title describes the bias as fictional. It is tagged "aprilfools". All of the citations are, even at a glance, either made up or about different biases. The post is peppered with weasel words in place of real references, like "As it turns out". The comments mention it's an April Fool's gag, and point to related real articles. The examples are completely absurd - and while the absurdity heuristic isn't perfect, "even though appearances can be misleading, they're usually not."

And the effect probably does really exist!

There are several lessons in there...

And yet, I was still fooled.

You have taught me not to change my mind so easily.


Grognor, I don't think it's fair to insinuate that you may have learned a wrong lesson here. If it's wrong (I actually doubt that it is), then it's up to you to try to resist learning it.

As regards walking readers into a trap to teach them lessons, one of my all-time favorite LW posts does exactly this, but is very forthcoming about it. By contrast, I think thomblake overestimates the absurdity of the examples here: I thought they seemed plausible, and that "Frodo Baggins" was just poor reasoning. The comments show I'm not alone here. This level of subtlety may be appropriate on April 1st, but by April 3rd, it's dated. I would recommend editing in a final line after the conclusion but before the references indicating that this post was an April Fool's joke.

I'm not so sure the lesson is wrong. I'm very confused by this particular meta level, and I don't think this confusion will ever actually be resolved.

Edit: but you're right, I implied that this was a bad lesson to learn and shouldn't have done that.

I would recommend editing in a final line after the conclusion but before the references indicating that this post was an April Fool's joke.

Done, with appropriate subtlety.

I would have believed everything you said if I hadn't read the comments. Now I'm going to subconsciously remember this article and use it as fictional evidence about the danger of fictional evidence.

A little subtle for my taste...


I understood the introductory question as "Frodo Baggins from the Lord of the Rings is buying pants. Which of these is he most likely to buy?", and correctly answered (c). I suggest rephrasing your question to ensure that it actually tests the reader's fictional bias. Also, Szalinski in Journal of Cognitive Minification is a nice one.

This deserves some time in the penalty box.

Am I the only one who didn't fall for it, and actually said "Wait, they didn't say it was THE Frodo, so really it's probably just some dude named Frodo and he probably wears a size 32/30."? I think it's actually a result of what we might call the "Ackbar effect" (it's a trap!); when presented with something that you expect to be an optical illusion, lateral-thinking puzzle, evidence of bias, etc. you immediately question your intuitive response or even force yourself into answering differently from your intuition. "I know those lines don't look parallel... but it's an optical illusion, so they must be." (You could then fool such people by giving them "illusions" that aren't; e.g. the lines don't look parallel because they really aren't parallel.)

There are such illusions that aren't: link (via Ironic Sans). These illusions appeared in the April 1971 issue of New Scientist magazine.

Of course they'd be in the APRIL issue.

Nice link. I was surprised to find that I'd upvoted this two years ago. I guess I don't remember most moments, in the long run.


Me too--I only remembered that it existed because it was the second LW post that I'd ever read.

Shame it's a fictional study, as the effect is almost certainly absolutely real and measurable. Study after study suggests that any association that pops up in your mind affects your behavior - I see no reason why fictional associations would be any less effective than all the other logically inapplicable associations which have been shown to have this kind of an effect. Here's an essentially randomly picked study on such things - it was just the first one I found googling for this kind of effect. The stereotype effect

Well, it is the case that people are biased by fiction. I'm thinking this fiction is going to bias some people into thinking people are not biased by fiction, and perhaps some other people, other way around.

This shows up as April 02 in my browser.

Hazards of living in Asia... it can be the morning of April 2nd where you live, and in the Western Hemisphere they're STILL playing April Fool's jokes.

I think that's the edit date - I posted it originally just after midnight April 1, EDT.

Dr. Sidney Zweibel and Dr. Emilio Lizardo

I don't know if i can trust a paper written by people with names like those... but then again, i'm probably just being irrational, just like you've explained.

(Try Googling those names.)


I take a look at the date and I wonder...

I expect that this 'bias' probably DOES have a real effect on people's thoughts and opinions, admittedly not as strong of one as in the 'evidence' provided by the article. Perhaps not for drugs, because fictional drugs tend to be bad instead of good in my experience and I don't think anybody names real drugs after fictional ones.
However, being named after a character in a popular work of fiction probably could change others' first impressions of you.

and I don't think anybody names real drugs after fictional ones.

A terrible 'marijuana substitute' is broadly marketed under the name "spice". [ D:< How dare they! ]

I read the first few sentences and was about to start formulating my enraged response, but then I looked at the date. Well played, my friend. Well played.

Pfft. And here I was hoping that I would harvest some good citations for the part of my essay which deals with exactly this subject - the pernicious distorting effect of fiction on our beliefs.

I should have remembered what day it was...

Look at the reference for the Szalinski paper. I'll bet it has a really small circulation...

Lesson learned: actually read the citations.

The journal that published Zweibel and Lizardo's paper's gotta be awesome...

I never even had a chance; it was March when I read it. :/ Guess I'll remove my downvote.

No, keep it down voted! The time stamp from where I'm sitting is April 2nd, and this is on the front page. Sowing random confusion as an "April 1st prank" is just senseless if you're not at least going to make sure the post is marked as such, and I honestly don't think such is appropriate here to begin with.

I actually think it's pretty useful for Less Wrong to have occasionally wrong articles that force us to maintain constant vigilance. I do think they should be labeled as such somewhere, but not obtrusively, to give people time to be "tested."

I was embarrassed that I failed the test (I tend to skim articles and say "yeah, sounds plausible", and I appreciated the "reality check."

While I agree with you in principle... - I know people who actually feel that it is amazingly clever to say things like this, and a lot of them self-identify as Rationalists. I don't feel that there is much benefit from determining whether I am dealing with someone who truly thinks like this, or merely a troll.

... so I really don't think this article qualifies as such a useful test. Why would I bother reading the citations if the article is already clearly bunk? It doesn't matter if he can back up his assertions, because the article is useless/wrong with or without that additional proof. If he'd made it a bit more obvious, perhaps, but this is pretty much indistinguishable from what I'd actually expect to see posted here occasionally (albeit normally under "Discussion" or at least not Promoted)


I appreciated it in part because there have been a few Less Wrong posts that HAD citations (or at least a bunch of links going to articles that looked fairly legit) which I took at face value, and I lazily threw the links at people without having read them thoroughly, only to find that they didn't say what I thought they said, or the evidence wasn't nearly as compelling.

It was a wake up call that you can't to outsource your rationality to someone else, even a community of rationalists. So essentially I try to always treat Lesswrong articles as if they are an April Fool's prank, either doublechecking them or not flagging them as "obvious truth" until I've read more background material.

I think having an occasional article that explicitly reminds of this is useful.

Hmmm, you make a fair point! I might not have valued the post, but that doesn't mean it wasn't valuable to others.

sorry if this is a random thought but i wonder whether this 'fictional bias' has guided the development of technology - as in seeing it in science fiction makes it seem more credible/real/potential/even needed and therefore scientists go out and make the technology to meet the fiction. realise this is not an exact match to the definition but it relates no? so if science fiction had come up with different technology would we have concentrated our efforts elsewhere and not be using mobile phones today for example.

I didn't fall for it either.

I assumed he just grabbed the name "Frodo Baggins" to represent a hypothetical male, unrelated to Lord of the Rings.

I got the answer right.... just because 30 is very small and 48 is very large, both seeming to represent smaller portions of society. I figured it was the 32 just based on probability of 'average size'.

For that matter, I couldn't stop my mind throwing up objections like "Frodo buys off-the-rack clothes? From where exactly? Surely he'd have tailor made? Wouldn't he be translated into British English as saying 'trousers'? Hobbit feet are big and hairy for Hobbits, but how big are they compared to human feet -- are their feet and inches 2/3 the size?"

It didn't occur to me until I'd read past the first two paragraphs that we were even theoretically supposed to ACTUALLY guess what size Frodo would wear. And I'm still unsure if the badness of the Frodo example was supposed to be part of the joke or not -- I mean, it's fairly funny if it is, but it's the sort of mistake (a bad example for a good point) I'd expect to see even made by intelligent, competent writers.

And I mean, I'm fairly sure that the fictional bias effect is real :)

But these could be written off as merely disturbed individuals. But as it turns out, we're affected by this bias in our daily lives.

Isn't that how it always is? Disturbed individuals have exaggerated biases relative to normal people, not entirely new ones.

Good joke. The references are especially good.

This looks like a particularly concrete and insidious instantiation of the narrative fallacy.