Saturday, 9 November 2013

Thinking, Fast and Slow (Daniel Kahneman)

Thinking, Fast and Slow is a 2011 book by Nobel Memorial Prize winner in Economics Daniel Kahneman which summarizes research that he conducted over decades, often in collaboration with Amos Tversky. It covers all three phases of his career:
- his early days working on cognitive bias,
- his work on prospect theory, and
- his later work on happiness.

The book's central thesis is a dichotomy between two modes of thought :
- System 1 is fast, instinctive and emotional;
- System 2 is slower, more deliberative, and more logical.
The book delineates cognitive biases associated with each type of thinking, starting with Kahneman's own research on loss aversion. From framing choices to substitution, the book highlights several decades of academic research to suggest that people place too much confidence in human judgment.

1 Prospect theory
2 Two systems
3 Heuristics and biases
3.1 Anchoring
3.2 Availability
3.3 Substitution
3.4 Optimism and loss aversion
3.5 Framing
3.6 Sunk-cost
4 Choices
5 Rationality and happiness
5.1 Two selves

The basis for his Nobel prize, Kahneman developed prospect theory to account for experimental errors he noticed in Daniel Bernoulli's traditional utility theory. This theory makes logical assumptions of economic rationality that do not reflect people’s actual choices, and does not take into account behavioral biases.

One example is that people are loss-averse: they are more likely to act to avert a loss than to achieve a gain. Another example is that the value people place on a change in probability (e.g. of winning something) depends on the reference point: people appear to place greater value on a change from 90% to 100% (going from high probability to certainty) than from, say, 45% to 55%, and place the greatest value of all on a change from 0% to 10% (going to a chance of winning from no chance). This despite that all three changes give the same increase in utility. Consistent with loss-aversity, the order of the first and third of those is reversed when the event is presented as losing rather than winning something: there, the greatest value is placed on eliminating the probability of a loss to 0.

Two systems

In the book's first section, Kahneman describes the two different ways the brain forms thoughts:
System 1: Fast, automatic, frequent, emotional, stereotypic, subconscious
System 2: Slow, effortful, infrequent, logical, calculating, conscious

Kahneman covers a number of experiments which purport to highlight the differences between these two thought processes, and how they arrive at different results even given the same inputs. Terms and concepts include coherence, attention, laziness, association, jumping to conclusions and how one forms judgments.

Heuristics and biases

The second section offers explanations for why humans struggle to think statistically. It begins by documenting a variety of situations in which we either arrive at binary decisions or fail to precisely associate reasonable probabilities to outcomes. Kahneman explains this phenomenon using the theory of heuristics.

Kahneman uses heuristics to assert that System 1 thinking involves associating new information with existing patterns, or thoughts, rather than creating new patterns for each new experience. For example, a child who has only seen shapes with straight edges would experience an octagon rather than a triangle when first viewing a circle. In a legal metaphor, a judge limited to heuristic thinking would only be able to think of similar historical cases when presented with a new dispute, rather than seeing the unique aspects of that case. In addition to offering an explanation for the statistical problem, the theory also offers an explanation for human biases.


The “anchoring effect” names our tendency to be influenced by irrelevant numbers. Shown higher/lower numbers, experimental subjects gave higher/lower responses. Experiment: experienced German judges proposed longer sentences if they had just rolled a pair of dice loaded to give a high number.


The availability heuristic is a mental shortcut that occurs when people make judgments about the probability of events by how easy it is to think of examples. The availability heuristic operates on the notion that, "if you can think of it, it must be important." The availability of consequences associated with an action is positively related to perceptions of the magnitude of the consequences of that action. In other words, the easier it is to recall the consequences of something, the greater we perceive these consequences to be. Sometimes, this heuristic is beneficial, but the frequencies that events come to mind are usually not accurate reflections of the probabilities of such events in real life.


System 1 is prone to substituting a simple question for a more difficult one. In what Kahneman calls their “best-known and most controversial” experiment, “the Linda problem.” Subjects were told about an imaginary Linda, young, single, outspoken and very bright, who, as a student, was deeply concerned with discrimination and social justice. They asked whether it was more probable that Linda is a bank teller or that she is a bank teller and an active feminist. The overwhelming response was that “feminist bank teller” was more likely than “bank teller,” violating the laws of probability. (Every feminist bank teller is a bank teller.) In this case System 1 substituted the easier question, "Is Linda a feminist?" dropping the occupation qualifier. An alternative view is that the subjects added an unstated implicature to the effect that the other answer implied that Linda was not a feminist.

Optimism and loss aversion

Kahneman writes of a "pervasive optimistic bias", which “may well be the most significant of the cognitive biases.” This bias generates the illusion of control, that we have substantial control of our lives. This bias may be usefully adaptive. Optimists are more psychologically resilient, have stronger immune systems, and live longer on average than more reality-based opposites. Optimism protects from loss aversion: people's tendency to fear losses more than we value gains.

A natural experiment reveals the prevalence of one kind of unwarranted optimism. The planning fallacy is the tendency to overestimate benefits and underestimate costs, impelling people to take on risky projects. In 2002, American kitchen remodeling was expected on average to cost $18,658, but actually cost $38,769.

To explain overconfidence, Kahneman introduces the concept he labels What You See Is All There Is (WYSIATI). This theory states that when the mind makes decisions, it deals primarily with Known Knowns, phenomena it has already observed. It rarely considers Known Unknowns, phenomena that it knows to be relevant but about which it has no information. Finally it appears oblivious to the possibility of Unknown Unknowns, unknown phenomena of unknown relevance.

He explains that humans fail to take into account complexity and that their understanding of the world consists of a small and not necessarily representative set of observations. Furthermore, the mind generally does not account for the role of chance and therefore falsely assumes that a future event will mirror a past event.


Framing is the context in which choices are presented. Experiment: subjects were asked whether they would opt for surgery if the “survival” rate is 90 percent, while others were told that the mortality rate is 10 percent. The first framing increased acceptance, even though the situation was no different.


Rather than consider the odds that an incremental investment would produce a positive return, people tend to "throw good money after bad" and continue investing in projects with poor prospects that have already consumed significant resources. In part this is to avoid feelings of regret.


In this section Kahneman returns to economics and expands his seminal work on Prospect Theory. He discusses the tendency for problems to be addressed in isolation and how, when other reference points are considered, the choice of that reference point (called a frame) has a disproportionate impact on the outcome. This section also offers advice on how some of the shortcomings of System 1 thinking can be avoided.

Rationality and happiness

Evolution teaches that traits persist and develop because they increase fitness. One possible hypothesis is that our conceptual biases are adaptive, as are our rational faculties. Kahneman offers happiness as one quality that our thinking process nurtures. Kahneman first took up this question in the 1990s. At the time most happiness research relied on polls about life satisfaction.

Two selves

Kahneman proposed an alternate measure that assessed pleasure or pain sampled from moment to moment, and then summed over time. Kahneman called this “experienced” well-being and attached it to a separate "self". He distinguished this from the “remembered” well-being that the polls had attempted to measure. He found that these two measures of happiness diverged. His major discovery was that the remembering self does not care about the duration of a pleasant or unpleasant experience. Rather, it retrospectively rates an experience by the peak (or valley) of the experience, and by the way it ends. Further, the remembering self dominated the patient's ultimate conclusion.

Kahneman demonstrated the principle using two groups of patients undergoing painful colonoscopies. Group A got the normal procedure. Group B, unknowingly received a few extra minutes of less painful discomfort after the end of the examination, i.e., more total discomfort. However, since Group B’s procedure ended less painfully, the patients in this group retrospectively minded the whole affair less.

“Odd as it may seem,” Kahneman writes, “I am my remembering self, and the experiencing self, who does my living, is like a stranger to me.”,_Fast_and_Slow

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