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Does Psychology Really Predict Behavior?
You keep using that word. I do not think it means what you think it means.
Posted January 30, 2018
What do the three following research findings have in common?
1. Computers can predict what you’re thinking based on your brain waves1. (Now I’m worried)
2. Immediate rewards predict sticking to new year’s resolutions2. (Now I’m hopeful)
3. Partner responsiveness predicts future health3. (Now I’m checking my own relationship)
In all these cases, psychology has claimed to predict something. The word predict makes psychology seem scientific and also makes people more likely to try to apply the findings. But what does psychology mean by 'predict'?
Prediction is a scale, anywhere from perfect prediction (100 percent accuracy) to random guessing.
In general conversation, people tend to reserve the word ‘predict’ for perfect prediction (100 percent accuracy). I’ve picked the Eurovision song contest winner 8 out of the last 10 times I watched it. Even my best friend won’t say I can predict the winner, just that I can often predict the winner.
However, in psychology, we say we predict something anytime the prediction is above the red zone of totally guessing. For the three examples at the start of this essay, I’ve plotted the amount of the prediction on the scale below (by using a binomial effect size display4).
I hope you can see the difference between perfect prediction and psychology’s prediction. These numbers aren’t terrible, they’re not terribly great either. Psychology is better than totally guessing but nowhere near the 100 percent prediction of our common usage.
When psychology says “X predicts Y”, what we really mean is that “X is one predictor of Y”. There can always be other predictors of the same behavior. For example, health isn’t solely predicted by partner responsiveness, nor would we expect or wish it to be.
Next week, I want to outline some different ways psychologists have thought about the reality of partial prediction. But, for now, I want you to relax and take psychology with a grain of salt. Psychology doesn’t perfectly predict things. Perhaps your past will predict your future, but perhaps it won’t.
For example, people often believe that how we attached to our early caregivers influences how well we do in adult romantic relationships5. Here’s where that is on the scale, with a comparison.
In some sense, you’d be better off asking me for the next Eurovision winner than believing your caregivers have sealed the fate of your romantic relationships. When psychology says prediction, we mean partial prediction, we never mean perfect prediction.
References
1. Suppes, P., Lu, Z-L., & Han, B. (1997). Brain wave recognition of words. Proceedings of the National Academy of Sciences, 94, 14965–14969.
2. Woolley, K., & Fishbach, A. (2017). Immediate rewards predict adherence to long-term goals. Personality and Social Psychology Bulletin, 43, 151-162.
3. Slatcher, R. B., Selcuk, E., & Ong, A. D. (2015). Perceived partner responsiveness predicts diurnal cortisol profiles 10 years later. Psychological Science, 26, 972-982.
4. Rosenthal & Rubin (1982) cited in Funder, (2013, pp. 93-95).
5. Steele, J., Waters, E., Crowell, J., & Treboux, D. (1998, June). Self-report measures of attachment: Secure bonds to other attachment measures and attachment theory? Paper presented at the biennial meeting of the International Society for the Study of Personal Relationships, Saratoga Springs, NY. (Cited by R. C. Fraley, 2000)
6. This is adjusted for the fact that I have to guess from 26 finalists.
