Chapter 12 → Judgment and Reasoning
Experience is an extraordinary teacher
Frequency Estimate → People’s assessment of how often an event has occurred in the past, or how
common an object is in the world.
Attribute Substitution → A commonly used strategy in which a person needs one type of information
but relies instead on a more accessible form of information. This strategy works well if the more
accessible form of information is, in fact, well correlated with the desired information. An example is the
case in which someone needs information about how frequent an event is in the world and relies instead
on how easily he or she can think of examples of the event
availability heuristic A particular form of attribute substitution in which the person needs to judge the
frequency of a certain type of object or the likelihood of a certain type of event. For this purpose, the
person is likely to assess the ease with which examples of the object or event come to mind; this
“availability” of examples is then used as an index of frequency or likelihood.
representativeness heuristic A strategy that is often used in making judgments about categories. This
strategy is broadly equivalent to making the assumption that, in general, the instances of a category will
resemble the prototype for that category and, likewise, that the prototype resembles each instance.
Table 12.1 Page 431
The Availability Heuristic
Heuristic → A strategy that is reasonably efficient and works most of the time. In using a heuristic, one is
in effect choosing to accept some risk of error in order to gain efficiency.
Sometimes we can be wrong (More R’s at start or middle… most choose start because thats whats is
“Available” to us in memory/ We can recall more. But really there are more R’s in the middle of words
than at the start
Recall 6 assertive times vs 12 assertive times… easier to recall 6 so you will think you’re more assertive
whereas those who can’t get all 12 will think they are less assertive.
We expect each individual to resemble the other individuals in the category (i.e., we expect each
individual to be representative of the category overall).
The Representativeness Heuristic
The category “birds,” for example, is reasonably uniform with regard to the traits of having wings, having
feathers, and so on. Virtually every member of the category has these traits, and so, in these regards, each
member of the category resembles all the others.
The representativeness heuristic capitalizes on this homogeneity
People think if you get a lot of heads when flipping a coin that a tail is due → Gambler's Fallacy… but a
coin as no memory so the chances will be 50/50 on every toss
The assumption of homogeneity can also lead to a different error—an expectation that the entire category
will have the same properties as the individual category members
Watching a video of prison guards nice/mean and then inferring that they are all that way Detecting Covariation
Covariation → A relationship between two variables such that the presence (or magnitude) of one
variable can be predicted from the presence (or magnitude) of the other. Co-variation can be positive or
negative. If it is positive, then increases in one variable occur when increases in the other occur. If it is
negative, then decreases in one variable occur when increases in the other occur.
Illusion of Covariation
People routinely “detect” covariation even where there is none
Knee pain/Bad weather
Confirmation bias → A family of effects in which people seem more sensitive to evidence that confirms
their beliefs than they are to evidence that challenges their beliefs. Thus, if people are given a choice
about what sort of information they would like in order to evaluate their beliefs, they request information
that is likely to confirm their beliefs. Likewise, if they are presented with both confirming and
disconfirming evidence, they are more likely to pay attention to, be influenced by, and remember the
confirming evidence, rather than the disconfirming.
Base-Rate Information → Information about the broad likelihood of a particular type of event (also
referred to as “prior probability”). Often contrasted with diagnostic information.
How frequently something occurs in general
Allows you to see if a drug works by comping it to the “Base Rate”
Ways of Thinking: Type 1, Type 2
Dual-Process Model → Any model of thinking that claims people have two distinct means of making
judgments—one of which is fast, efficient, but prone to error, and one that is slower, more effortful, but
also more accurate.
Type 1 → A commonly used name for judgment and reasoning strategies that are fast and effortless, but
prone to error.
Type 2 → A commonly used name for judgment and reasoning strategies that are slower and require
more effort than Type 1 strategies, but are less prone to error.
One hypothesis is that people choose when to rely on each system; presumably, they shift to the less
efficient, more accurate Type 2 when making a judgment that really matters. As we’ve seen, however,
people rely on Type 1’s heuristics even when incentives are offered for accuracy, even when making
important professional judgments, even when making medical diagnoses that may, in some cases, literally
be matters of life and death. Surely people would choose to use Type 2 in these cases if they could, yet
they still rely on Type 1 and fall into error. On these grounds, it’s difficult to argue that using Type 2 is a
matter of deliberate choice.
Codable Data Better quality judgements are more likely if the role of random chance is conspicuous in a problem.
People are more likely to see that the evidence could be a fluke or accident and not be a reliable pattern…
people are then more likely to pay attention to the quantity of evidence on the (sensible) idea that a larger
set of observations is less vulnerable to chance fluctuation.
People are more accurate in their judgments, and less prone to heuristic use, when confronting evidence
that is easily understood in statistical terms
How well pe