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Inevitable Illusions

Page history last edited by PBworks 13 years, 7 months ago
Notes on: Massimo Piatelli-Palmarini (1994). Inevitable Illusions: How mistakes of reason rule our minds. New York: Wiley
This book explains research on heurisitics and biases (in judgement and decision-making) in an accessible way, with a view to helping readers de-bias their own mental processes.
It centres around two strong and appealing analogies. The first is the analogy between cognitive biases and optical illusions. Because of the way human perception works, we can be misled in certain circumstances into seeing one colour as darker than another, or one line longer than another. In the same way, our estimation of likelihoods of an event, or our preference between two choices, can be disconnected from reality and manipulated.
The second analogy is between trying to live a virtuous life and trying to minimise the effects of bias on our own decisions.
Some of the illusions are introduced using "Tunnels of the Mind". These are problems to which there is an "obvious" solution which, when worked out carefully, turns out to be wrong. The "Super-Tunnel" presented at the end of the book is the Monty Hall Puzzle, where the clash between instinct and probability is at its most palpable.
There is not much mention of egotistical biases or other value biases in the book: the focus is on the heuristics and biases tradition associated with Tversky and Kahneman, rather than on cognitive dissonance, although there are dissonance explanations for some of the biases that Piatelli-Palmarini talks about.


Eight Properties of Cognitive Illusions


  1. General: pervasive in human thought & decision-making
  2. Systematic: reproducible in different subjects and situations
  3. Directional: biases rather than uncertainties (see my Varieties of Bias)
  4. Specific: illusions reveal themselves in specific conditions
  5. Externally modulable: variations in the context affect the illusion in systematic and predictable ways.
  6. Subjectively incorrigible: when subjects learn about errors, they do not necessarily stop making them.
  7. Nontransferable: learning to avoid error in one kind of task does not mean we will also avoid error in logically similar tasks.
  8. Independent of intelligence and education: even experts are affected


Seven Deadly Sins (of the Illusion of Knowing)


(I'm not 100% sure these are seven distinct categories: the distinctions between 2, 5 and 6 are questionable)

  1. Overconfidence
    • Fischoff et al. (1977) experiment using general knowledge questions: Subjects overestimate how many of their answers are correct. Subjects express 99%, 99.9% or even greater confidence in answers which are in fact wrong. Attempts to "debias" the subjects (by lecturing them on probability) are only slightly successful.
  2. Illusory correlations (magical thinking) (demonstrated by, inter alia, the Wason selection task); lack of Four-Cells thinking (as I call it)
  3. Predictability in hindsight (otherwise known as hindsight bias)
  4. Anchoring (information that we know to be unreliable still influences our judgements, because we try not to stray far from it)
  5. Ease of representation (i.e. Availability heuristic)
    • (e.g. people wrongly think that deaths from fireworks are more common than deaths from diabetes, because deaths from fireworks get more publicity) The emotional impressionability of an event or pattern does not have much connection with its objective occurrence.
  6. Probability Blindness
    • Including ignorance of base rates, treating different probabilities as though they were the same; treating a one-in-a-million risk the same as a 50-per-cent risk; confusing what is typical with what is probable (e.g. regarding HHHHHH as less probable than HTTHTH)
  7. Reconsideration under suitable scripts (otherwise known as framing effects)
    • e.g. Conjunction Fallacy
    • The subjective probability of a far-fetched possibility can be raised by giving people a "plausible" story, even if that story depends on a succession of implausible assumptions.

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