Availability cascade
An availability cascade is a self-reinforcing cycle that explains the development of certain kinds of collective beliefs. A novel idea or insight, usually one that seems to explain a complex process in a simple or straightforward manner, gains rapid currency in the popular discourse by its very simplicity and by its apparent insightfulness. Its rising popularity triggers a chain reaction within the social network: individuals adopt the new insight because other people within the network have adopted it, and on its face it seems plausible. The reason for this increased use and popularity of the new idea involves both the availability of the previously obscure term or idea, and the need of individuals using the term or idea to appear to be current with the stated beliefs and ideas of others, regardless of whether they in fact fully believe in the idea that they are expressing. Their need for social acceptance, and the apparent sophistication of the new insight, overwhelm their critical thinking.
The idea of the availability cascade was first developed by Timur Kuran and Cass Sunstein as a variation of information cascades mediated by the availability heuristic, with the addition of reputational cascades. The availability cascade concept has been highly influential in finance theory and regulatory research, particular with respect to assessing and regulating risk.
Cascade elements
Availability cascades occur in a society via public discourse or over social networks—sets of linked actors in one or more of several roles. These actors process incoming information to form their private beliefs according to various rules, both rational and semi-rational. The semi-rational rules include the heuristics, in particular the availability heuristic. The actors then behave and express their public beliefs according to self-interest, which might cause their publicly expressed beliefs to deviate from their privately held beliefs.Kuran and Sunstein emphasize the role of availability entrepreneurs, agents willing to invest resources into promoting a belief in order to derive some personal benefit. Other availability entrepreneurs with opposing interests may wage availability counter-campaigns. Other key roles include journalists and politicians, both of which are subject to economic and reputational pressures, the former in competition in the media, the latter for political status. As resources are limited, beliefs compete with one another in the "availability market". A given incident and subsequent availability campaign may succeed in raising the availability of one issue at the expense of other issues.
Belief formation
posits that human reasoning is divided into two systems, often called System 1 and System 2. System 1 is automatic and unconscious; other terms used for it include the implicit system, the experiential system, the associative system, and the heuristic system. System 2 is evolutionarily recent and specific to humans, performing the more slow and sequential thinking. It is also known as the explicit system, the rule-based system, the rational system, or the analytic system. In The Happiness Hypothesis, Jonathan Haidt refers to System 1 and System 2 as the elephant and the rider: while human beings incorporate reason into their beliefs, whether via direct use of facts and logic or their application as a test to hypotheses formed by other means, it is the elephant that is really in charge.Cognitive biases
are simple, efficient rules which people often use to form judgments and make decisions. They are mental shortcuts that replace a complex problem with a simpler one. These rules work well under most circumstances, but they can lead to systematic deviations from logic, probability or rational choice theory. The resulting errors are called "cognitive biases" and many different types have been documented. These have been shown to affect people's choices in situations like valuing a house or deciding the outcome of a legal case. Heuristics usually govern automatic, intuitive judgments but can also be used as deliberate mental strategies when working from limited information. While seemingly irrational, the cognitive biases may be interpreted as the result of bounded rationality, with human beings making decisions while economizing time and effort.Kuran and Sunstein describe the availability heuristic as more fundamental than the other heuristics: besides being important in its own right, it enables and amplifies the others, including framing, representativeness, anchoring, and reference points.
Availability heuristic
Even educated human beings are notoriously poor at thinking statistically. The availability heuristic, first identified by Daniel Kahneman and Amos Tversky, is a mental shortcut that occurs when people judge 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." Availability can be influenced by the emotional power of examples and by their perceived frequency; while personal, first-hand incidents are more available than those that happened to others, availability can be skewed by the media. In his book Thinking, Fast and Slow, Kahneman cites the examples of celebrity divorces and airplane crashes; both are more often reported by the media, and thus tend to be exaggerated in perceived frequency.Examples
An important class of judgments is those concerning risk: the expectation of harm to result from a given threat, a function of the threat's likelihood and impact. Changes in perceived risk result in risk compensation—correspondingly more or less mitigation, including precautionary measures and support for regulation. Kuran and Sunstein offer three examples of availability cascades—Love Canal, the Alar scare, and TWA Flight 800—in which a spreading public panic led to growing calls for increasingly expensive government action to deal with risks that turned out later to be grossly exaggerated. Others have used the term "culture of fear" to refer to the habitual achieving of goals via such fear appeals, notably in the case of the threat of terrorism.Disease threats
In the early years of the HIV/AIDS epidemic, many believed that the disease received less attention than warranted, in part due to the stigma attached to its sufferers. Since that time advocates— availability entrepreneurs that include LGBT activists and conservative Surgeon General of the United States C. Everett Koop—have succeeded in raising awareness to achieve significant funding. Similarly, awareness and funding for breast cancer and prostate cancer are high, thanks in part to the availability of these diseases. Other prevalent diseases competing for funding but lacking the availability of HIV/AIDS or cancer include lupus, sickle-cell anemia, and tuberculosis.Vaccination scares
The MMR vaccine controversy was an example of an unwarranted health scare. It was triggered by the publication in 1998 of a paper in the medical journal The Lancet which presented apparent evidence that autism spectrum disorders could be caused by the MMR vaccine, an immunization against measles, mumps and rubella.In 2004, investigations by Sunday Times journalist Brian Deer revealed that the lead author of the article, Andrew Wakefield, had multiple undeclared conflicts of interest, had manipulated evidence, and had broken other ethical codes. The Lancet paper was partially retracted in 2004 and fully retracted in 2010, and Wakefield was found guilty of professional misconduct. The scientific consensus is that no evidence links the vaccine to the development of autism, and that the vaccine's benefits greatly outweigh its risks.
The claims in Wakefield's 1998 The Lancet article were widely reported; vaccination rates in the UK and Ireland dropped sharply, which was followed by significantly increased incidence of measles and mumps, resulting in deaths and severe and permanent injuries. Reaction to vaccine controversies has contributed to a significant increase in preventable diseases including measles and pertussis, which in 2011 experienced its worst outbreak in 70 years as a result of reduced vaccination rates.
Concerns about immunization safety often follow a pattern: some investigators suggest that a medical condition is an adverse effect of vaccination; a premature announcement is made of the alleged adverse effect; the initial study is not reproduced by other groups; and finally, it takes several years to regain public confidence in the vaccine.