The Conjunction Fallacy
Humans are required to make thousands of decisions every day. To do this, people often use mental shortcuts called heuristics. These mental shortcuts often work well but can sometimes ignore logic and probability. When a person believes a specific condition is more probable than a general one, they are being affected by the conjunction fallacy. The conjunction fallacy is also known as the Linda problem because of a study done by Amos Tversky and Daniel Kahneman that started in 1974. The probability of a conjunction is not more likely than either of its parts but the conjunction fallacy causes a person to feel otherwise.
The study by Tversky and Kahneman (1983), known as the Linda problem, was the study that first brought attention to the conjunction fallacy. In this study, participants were given a description of a fictitious woman named Linda. The participants were told to guess from a list of occupations and associations and choose which one was most probable for Linda. Among these options were bank teller, active in the feminist movement, and bank teller who is active in the feminist movement. The description of Linda made her seem like a good fit to be active in the feminist movement but a poor fit for a bank teller. However, 85% of participants ranked the probability of Linda being a bank teller who is active in the feminist movement higher than her being a bank teller. This supports the conjunction fallacy because people believed it was more likely that Linda would be a feminist bank teller rather than a bank teller, even though the latter is more likely.
Another, smaller study by Tversky and Kahneman (1980) had participants make an attempt at predicting the results of the upcoming Wimbledon. When this study was done, there was a great player named Bjorn Borg who had won Wimbledon the past 5 years. 93 people were asked to rank 4 statements from most likely to least likely supposing Bjorn Borg went to the Wimbledon finals the following year. Among the statements were, Borg will win the match, Borg will lose the first set, and Borg will lose the first set but win the match. Most people ranked Borg losing the first set but winning the match higher than Borg losing the first set. This supports the conjunction fallacy because people believed the more specific statement – Borg losing the first set but winning the match over a more general statement- Borg losing the first set, even though the last option is more likely.
Lastly, a study done by Charles Hsee (1998) demonstrated a subdivision of the conjunction fallacy called the less-is-more-effect in 3 different scenarios. In the first scenario, participants were asked who was more generous, a person gifting a $45 scarf or a person gifting a $55 coat. Most participants said the person donating the scarf was more generous even though the scarf was $10 less than the coat. This connects to the conjunction fallacy because the option that is less in value is considered to be greater than the larger value option. In the second scenario, the participants were shown two vendors and the amount of ice cream they sold. Vendor A sold 8oz (237mL) of ice cream in a 10oz (296mL) cup. Vendor B sold 7oz (207mL) in a 5oz in a (148mL ) cup. The participants were then asked what they were willing to pay for each. Most participants were willing to pay around the same for each ice cream when viewed together but when only viewing one, Vendor B’s ice cream was valued as more. This connects to the conjunction fallacy because the option that is less in value is considered similar or greater than the option that has more value. Finally, in the last scenario, the participants were shown 2 sets of dinnerware. The first set of dinnerware contained 8 dinner plates, 8 bowls, and 8 dessert plates. The second set contained the same items but 7 intact cups plus 1 broken one and 1 intact saucer and 7 broken ones. When viewing both sets, participants gave a higher price to the second set, however, when viewed alone it was ranked much lower. This connects to the conjunction fallacy because the more that a person can get (or more specific) the higher they will rank it, even if there is less quality (or less probability).
In conclusion, the conjunction fallacy has been proven in numerous studies that are easy to replicate and it can be seen in everyday life. The knowledge and exploitation of this fallacy is common practice in the world of sales. In short, the conjunction fallacy is a mental shortcut created by our brains convincing us that less is, in fact, more.
Hsee, C. (n.d.). The less is more effect. Retrieved from https://poseidon01.ssrn.com/delivery.php?ID=891007123000074079098093031025123064123050031074004004104069126077101113022003123070120025020125015023028112124029065016097022057000058021115002007111031069123041078057118031072105082118079029117031122066112096068116027114120026088088081068004119&EXT=pdf
Kahneman, D. (2011). Thinking fast and slow. New York: Farrar, Straus & Giroux. https://doi.org/10.1086/674372
Kahneman, D., & Tversky, A. (n.d.). The linda problem. Retrieved from http://psycnet.apa.org/fulltext/1984-03110-001.pdf
Kahneman, D., & Tversky, A. (1983). Existential versus intuitive reasoning: The conjunction fallacy in probability judgement. Psychological Review, 90(4). Retrieved from http://faculty.econ.ucdavis.edu/faculty/nehring/teaching/econ106/readings/Extensional%20Versus%20Intuitive.pdf
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