A while back Jon Sutton at The Psychologist asked my opinion on the end of history illusion. This was sparked by an interesting Science paper by Quoidbach, Gilbert and Wilson. Blogger and mathematician Jordan Ellenberg had written a blog post arguing that the paper makes a mistake: "a somewhat subtle mistake, but a bad mistake, and one which kills a big chunk of the paper".
Jon wanted a second opinion, and after a bit of reading I replied that Ellenberg's criticisms were valid. I meant to blog about it at the time but got caught up in other things. Consequently I missed the BPS research digest piece on it.
The reason for writing this blog post is because the flaw that Ellenberg spotted is quite interesting in its own right and because both the description by Ellenberg and the description in the Research Digest article probably don't explain it clearly enough for some readers to appreciate. Ellenberg's piece is (I hasten to add) crystal clear but relies on a reader being comfortable with the formal, mathematical approach he takes (which many psychologists won't be). The Research Digest description just gives the brief gist (with a link to Ellenberg for the full picture). Here is my belated attempt at a psychologist-friendly interpretation with no formal notation - and as little maths as possible.
According to the end of history illusion people underestimate how much they will change in the future. For example, someone asked to predict how their personality would change in the next ten years would come up with a prediction closer to their original position than their actual position. Quoidbach et al. tested this mainly by asking people to predict future values on some psychological variable (e.g., a personality test score) and then showing that actual change is much greater than the difference between the original and predicted scores. This seems highly plausible, but Ellenberg pointed out that the difference in the predicted and original scores is a different quantity from the expected (absolute) change in scores.
Why is this? Perhaps the easiest way to understand is to work through a simple example. Imagine that my extraversion score is 50 on a scale that goes from 0 (extremely introverted) to 100 (extremely extraverted). A researcher then asks me to predict my extraversion score in 10 years time. I, being a keen observer of human nature (bear with me on this if you know me - it is just an example), am aware that personality is not fixed and judge that I am likely to change quite a bit - say 15 points - on the scale. However, I might get more extraverted or I might get more introverted (depending on how life treats me over the next ten years). Given that I'm in the middle of the scale, I could end with a score of 35 or a score of 65. Thus I predict that my extraversion score after 10 years will be (35 + 65)/2 = 50. It looks as though I've predicted zero change, when what I've done is give the best prediction I can (one that minimizes my prediction error). Had I instead been asked to give the absolute change I expected, my answer would have been different. It would have been (15 + 15)/2 = 15 (not zero).
Although the example is simple it captures the essence of the problem. Commenters on Ellenberg's blog looked again at the raw data that Quoidback et al. provided. According to their analyses the end of history illusion largely disappears when analyzed correctly (though only some of the data sets support such a reanalysis). Thus if the end of history illusion effect exists (and the basic premise seems highly plausible) it is quite probably a much smaller and more fragile effect than originally thought. That makes sense to me - because I'm not sure that such a bias could be both pervasive and large in the face of the counter-evidence available to people about past change in themselves and change in others.
My continued interest in the effect is slightly different. There seems to be a cognitive illusion at work here - one that makes the difference between the original score and predicted score appear to be a good measure of an entirely different quantity - the expected absolute change in score ...
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