Psychology of rule of thumb

The origin of the phrase ‘rule of thumb’ is uncertain. It might have evolved from the use of the thumb as a measurement device ("rule"). Some claim that it comes from beer brewing before the invention of thermometers, when brewers would use their thumbs to measure the temperature of batches of beer.

In Greek the rule of thumb is heuristic, which is term used in philosophy and psychology. In cognitive psychology it refers to experience-based techniques applied to various cognitive processes like problem solving, learning, and logical thinking. In situations where an exhaustive search is impractical, rule of thumb or heuristic methods are used to speed up the process of finding a satisfactory solution. The terms such as educated guess, intuitive judgment and commonsense are considered as equivalent to heuristics.  In more precise terms, heuristics are strategies using readily accessible information to problem solving.

Cognitive biases

In psychology, heuristics refers to simple, efficient rules which are inbuilt upon the mental processes of the individual through evolutionary processes or learning. These rules have been proposed to explain how people make decisions, come to judgments, and solve problems, typically when facing complex problems or using incomplete information. These rules work well under most circumstances, but in certain cases lead to errors. These errors are due to cognitive biases.

A cognitive bias is a deviation in judgment that occurs in particular situations. This deviation from the normally expected thinking process leads to distorted or erroneous perception, inaccurate judgment, illogical interpretation, or what is broadly called irrationality. The concept of “deviation" refers to a standard of comparison with what is normally expected from an individual in a particular situation. This comparison may be with the judgment of people those who are outside the particular situation, or with a set of facts which can be objectively verified by others. A long and ever-growing list of cognitive biases has been identified over the last six decades of research on human judgment and decision-making in cognitive science, social psychology, and behavioral economics.

Cognitive biases are examples of mental behavior which are evolved in the course of the individual’s life or inbuilt by the evolution of the human species. Many of the cognitive biases are evidently adaptive because they lead to more effective actions in given contexts or enable faster decisions when faster decisions are of greater value for survival. These are called adaptive biases.

Adaptive bias is the idea that the human brain has evolved to gain the cognitive ability of reason adaptively, rather than rationally, and that cognitive bias may have evolved as a mechanism to reduce the overall cost of cognitive errors as opposed to merely reducing the number of cognitive errors, when faced with making a decision under conditions of uncertainty.

Example of adaptive bias

The ambiguity effect is an example of adaptive bias. The situation of ambiguity is created by lack of sufficient information. The decision making in such situations is affected by lack of information, or "ambiguity". People tend to select options for which the probability of a favorable outcome is known, over an option for which the probability of a favorable outcome is unknown.

The 30-ball-experiment has proved the existence of ambiguity effect in human thinking. The test is as follows: A bucket contains 30 balls. The balls are colored red, black and white. There is definite information that ten of the 30 balls are red. Of the remaining 20 some are white and some are black, with all combinations of black and white being equally likely. That is all the combinations like 1:19, 2:18, 2:17…. And 19:1are equally possible. The participants should take a ball blindly from the bucket after selecting an option. In option X, drawing a red ball wins a person $100, and in option Y, drawing a black ball wins them $100. The probability of picking a winning ball is the same for both options X and Y. In option X, the probability of selecting a winning ball is 1 in 3 (10 red balls out of 30 total balls). In option Y there is uncertainty of the outcome because there is no information how many balls are black and how many are white. The difference between the two options is that in option X, the probability of a favorable outcome is known, but in option Y, the probability of a favorable outcome is unknown ("ambiguous"). But there is a chance in option Y the probability could be more than that in X because the combination of Black : White could be 19:1. If so, the chance of winning is 2 in 3. In spite of the chance for high probability of a favorable outcome, people have a greater tendency to select a ball under option X, where the probability of selecting a winning ball is perceived to be more certain. The uncertainty as to the number of black balls means that option Y tends to be viewed less favorably. Despite the fact that there could possibly be twice as many black balls as red balls, people tend not to want to take the opposing risk that there may be fewer than 10 black balls. The "ambiguity" behind option Y means that people tend to favor option X, even when the probability is equivalent.

One possible explanation of the effect is that people have a rule of thumb (heuristic) to avoid options where information is missing or where there is ambiguity. This will often lead them to seek out the missing information. In many cases, though, the information cannot be obtained. The effect is often the result of calling some particular missing piece of information to the person's attention. The ambiguity effect evidently helped the survival in natural conditions.

Assessment of probability by rule of thumb

In daily life people take decisions after assessing probability of outcome in situations of uncertainty and ambiguity.  In assessing probability people use the rule of thumb. Example: I am going to toss a coin for six times. Before actually doing it I am presenting two probabilities. Probability one: Head, Head, Head, Tail, Tail, Tail. Probability two: Head, Tail, Tail, Head, Tail, Head, Head. Which outcome is more probable? A trained statistician would say both are equally probable. But almost all non professionals would say the second outcome is more probable, because it appears to be the representative of the outcomes in the random events. People predict those which have a representativeness appearance more probable. This rule of thumb is called representativeness heuristic.

Availability in mind

Another rule of thumb in assessment of probability is whatever available in mind is thought to be more probable.  This is called availability heuristic. The availability heuristic is a mental shortcut that uses the ease with which examples come to mind to make judgments about the probability of events. 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 act is positively related to perceptions of the magnitude of consequences of that act. Sometimes, this heuristic is beneficial, but the frequency that events come to mind is usually not accurate reflections of their actual probability in reality.

Media mislead in assessment of probability

Media coverage can help fuel a person's example bias with widespread and extensive coverage of unusual events, such as homicide or airline accidents, and less coverage of more routine, less sensational events, such as common diseases or car accidents. For example, when asked to rate the probability of a variety of causes of death, people tend to rate more "newsworthy" events as more likely because they can more readily recall an example from memory. For example, in the USA, people rate the chance of death by homicide higher than the chance of death by stomach cancer, even though death by stomach cancer is five times higher than death by homicide. Moreover, unusual and vivid events like homicides, shark attacks, or lightning are more often reported in mass media than common and unsensational causes of death like common diseases. Another instance of biased ratings is the relative overestimation of plane crash deaths, compared to car-accident deaths.

Psychology of bandwagon effect and other cognitive biases

Cognitive bias is a deviation from what leads to correct decision in a particular situation. Cognitively biased deviation leads to errors in various spheres of life. The following are the common errors occurring due to cognitive biases.

Bandwagon effect

Let us first consider the meaning and origin of the term. Literally, a bandwagon is a wagon which carries the band in a parade, circus or other entertainment. The phrase "jump on the bandwagon" first appeared in American politics in 1848 when Dan Rice, a famous and popular circus clown of the time, used his bandwagon and its music to gain attention for his political campaign appearances. As his campaign became more successful, other politicians strove for a seat on the bandwagon, hoping to be associated with his success. Later, during the time of William Jennings Bryan's 1900 presidential campaign, bandwagons had become standard in campaigns, and "jump on the bandwagon"  was used as a derogatory term, implying that people were associating themselves with the success without considering what they associated themselves with.

The bandwagon effect is a form of groupthink in social psychology. The general rule is that conduct or beliefs spread among people, as fads and trends do, with the probability of any individual adopting it. As more people come to believe in something, others also "jump on the bandwagon" regardless of the underlying evidence. The tendency to follow the actions or beliefs of others can occur because individuals directly prefer to conform, or because individuals derive information from others. Both explanations have been used for evidence of conformity in psychological experiments. When individuals make rational choices based on the information they receive from others, economists have proposed that information cascades can quickly form in which people decide to follow the behavior of others. Cascades explain why behavior is fragile—people understand that they are based on very limited information. As a result, fads form easily but are also easily dislodged. Such informational effects have been used to explain political bandwagons.

The bandwagon effect occurs in voting: some people vote for those candidates or parties who are likely to succeed (or are proclaimed as such by the media), hoping to be on the "winner's side" in the end. The bandwagon effect has been applied to situations involving majority opinion, such as political outcomes, where people alter their opinions to the majority view. Such a shift in opinion can occur because individuals draw inferences from the decisions of others, as in an informational cascade.

Attentional Bias

We normally give increased attention or hyper-attention to both attractive and threatening materials. In cognitive psychology attentional bias refers to hyper-attention to threatening materials. The threat may be unrealistic. For example a person with arachnophobia (fear of spider) always shows attentional bias not only to spider but also anything related to spider. This hyper-attention occurs even with verbal material such as words like spider, web, creeping etc. Psychologists use modified Stroop test to demonstrate attentional bias in persons with phobias.

When the name of a color (e.g., "blue," "green," or "red") is printed in a color not denoted by the name (e.g., the word "red" printed in blue ink instead of red ink), naming the color of the word takes longer and is more prone to errors than when the color of the ink matches the name of the color. The effect is named after American psychologist John Ridley Stroop (1897 – 1973) who first published the effect in 1935. The effect has been used to create a psychological test (Stroop Test) that is widely used in clinical practice and investigation.

To establish the attention bias in persons with phobia the Stroop Test is used in a different manner. If the person is suffering from spider phobia words related to spider such as “spider”, “web”, “creepy” are printed in different colours and the person is asked to name the colour of the word. If the person is phobic to spider he/she takes longer time to name the colour because he/she gives hyper-attention to the feared object. Reduction of attention bias through frequent exposure of the feared object is the remedy for this type of disorders. The modified Stroop Test is also used for measuring the improvement in the condition.

Attentional bias phenomena have been found to occur not only in a number of anxiety disorders (e.g., specific phobia, panic disorder, generalized anxiety disorder), but also individuals with anxiety by trait. It appears that these traits point in the direction of a hyper-vigilant cognitive style that gives high processing priorities to threat-related stimuli, thereby promoting escalation of fear.

Belief bias

In everyday life people have to evaluate the validity of opinions given or conclusions arrived at by others. People accept or reject these conclusions or opinions depending if they are consistent with their everyday knowledge or prior beliefs. This cognitive process is called belief bias. Belief bias occurs when there is a conflict between existing belief or knowledge and the logical conclusion.

Let us consider the following logical conclusion:

All dogs are animals.

All animals have four legs.

Therefore, all dogs have four legs.

There is no conflict between existing knowledge or belief and the logical conclusion. Let us consider another logical conclusion.

All poodles are dogs.

All dogs are animals.

Therefore, all animals are poodles.

This logical conclusion contradicts with existing common knowledge and therefore it is considered as invalid.

People accept any and all conclusions that happen to fit with their system of beliefs. Beliefs and meaning, not the statistical analysis and other abstract systems invented by philosophers, lie at the core of human thinking. The supremacy of meaningful beliefs appears to be universal. Famous Russian neuro-psychologist Alexander Romanovich Luria asked illiterate farmers from Central Asia o reason deductively, giving them syllogisms of the following sort: “In the Far North, where there is snow, all bears are white. Novaga Zmlya  is in the Far North. What color are the bears there?”  The responses were of this sort: “I don’t know; I’ve seen a black bear, I’ve never seen any others…. Each locality has its own animals; it it’s white, they will be white; if it’s yellow, they will be yellow”. Some responses were: “How can I know?” Luria observed that the farmers simply ignored or forgot premises that contradicted their own knowledge.  

Confirmation bias

Confirmation bias (also called my-side bias or verification bias) is an ally of belief bias. It is a tendency of people to favor information that confirms their beliefs or hypotheses. People display this bias when they gather or remember information selectively, or when they interpret it in a biased way. The effect is stronger for emotionally charged issues and for deeply entrenched beliefs. For example, in reading about gun control, people usually prefer sources that affirm their existing attitudes. They also tend to interpret ambiguous evidence as supporting their existing position. Biased search, interpretation and memory have been invoked to explain attitude polarization, belief perseverance or continuing existing beliefs after the evidence for them is shown to be false, the irrational primacy effect or a greater reliance on information encountered first in a series and illusory correlation or falsely perceiving an association between two events or situations. Confirmation biases contribute to overconfidence in personal beliefs and can maintain or strengthen beliefs in the face of contrary evidence. Poor decisions due to these biases have been found in military, political, and organizational contexts.

Confirmation bias has been described as an internal "yes-man", echoing back a person's beliefs like Uriah Heep. Uriah Heep is a fictional character created by Charles Dickens in his novel David Copperfield. The character is notable for his cloying humility, obsequiousness, and insincerity, making frequent references to his own "'humbleness". His name has become synonymous with being a yes-man.