Belief bias is the tendency to judge the strength of arguments based on the plausibility of their conclusion rather than how strongly they support that conclusion. In other words, if people agree with a viewpoint, they are inclined to believe that the process used to obtain the results must also be correct.
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Syllogisms
A syllogism is a kind of logical argument in which one proposition (the conclusion) is inferred from two or more others (the premises) of a specific form. The classical example of a valid syllogism is:
An example of an invalid syllogism is:
Typically, a majority of test subjects in studies incorrectly identify this syllogism as one in which the conclusion follows from the premises. It might be true in the real world that a) girls study and b) this is because they are ambitious. However, this argument is a fallacy, because the conclusion is not supported by its premises. The validity of an argument is different from the truth of its conclusion: there are valid arguments for false conclusions and invalid arguments for true conclusions. Hence, it is an error to judge the validity of an argument from the plausibility of its conclusion. This is the reasoning error known as belief bias.
When a person gives a response that is determined by the believability of the conclusion rather than logical validity, this is referred to as belief bias only when syllogism are used. This phenomenon is so closely related to syllogistic reasoning that when it does occur, in areas such as Wason's selection task or the THOG problem, it is called "memory cueing" or the "effects of content".
Research
In a series of experiments by Evans, Barston and Pollard (1983), participants were presented with evaluation task paradigms, containing two premises and a conclusion. The participants were asked to make an evaluation of logical validity. The subjects, however, exhibited a belief bias, evidenced by their tendency to reject valid arguments with unbelievable conclusions, and endorse invalid arguments with believable conclusions. Instead of following directions and assessing logical validity, the subjects based their assessments on personal beliefs.
Consequently, these results demonstrated a greater acceptance of more believable (80%), than unbelievable (33%) conclusions. Participants also illustrated evidence of logical competences and the results determined an increase in acceptance of valid (73%) than invalid (41%). Additionally, there’s a small difference between believable and valid (89%) in comparison to unbelievable and invalid (56%) (Evans, Barston & Pollard, 1983; Morley, Evans & Handley, 2004).
It has been argued that using more realistic content in syllogisms can facilitate more normative performance from participants. It has been suggested that the use of more abstract, artificial content will also have a biasing effect on performance. Therefore, more research is required to understand fully how and why belief bias occurs and if there are certain mechanisms that are responsible for such things. There is also evidence of clear individual differences in normative responding that are predicted by the response times of participants.
A 1989 study by Markovits and Nantel gave participants four reasoning tasks. The results indicated “a significant belief-bias effect” that existed “independently of the subjects' abstract reasoning ability.”
A 2010 study by Donna Torrens examined differences in belief bias among individuals. Torrens found that “the extent of an individual's belief bias effect was unrelated to a number of measures of reasoning competence” but was, instead, related to that person's ability “to generate alternative representations of premises: the more alternatives a person generated, the less likely they were to show a belief bias effect."
In a 2010 study, Chad Dube and Caren M. Rotello of the University of Massachusetts and Evan Heit of the University of California, Merced, showed that “the belief bias effect is simply a response bias effect.”
In a 2012 study, Adrian P. Banks of the University of Surrey explained that “belief bias is caused by the believability of a conclusion in working memory which influences its activation level, determining its likelihood of retrieval and therefore its effect on the reasoning process.”
Michelle Colleen and Elizabeth Hilscher of the University of Toronto showed in 2014 that belief bias can be affected by the difficulty level and placement of the syllogism in question.