A common error that occurs with everyday thinking is Myside Bias — the tendency for people to evaluate evidence, generate evidence, and test hypotheses in a manner biased toward their own opinions.

Measures of intelligence, often considered synonymous with good thinking, do not assess the avoidance of myside bias (Stanovich & West, 2008; Sternberg, 2001). Intelligence (as measured by popular intelligence tests and their proxies) shows a weak association with avoidance of myside bias, and in some instances, particularly under conditions where explicit instructions have not been given to avoid myside bias, shows no association with the avoidance of this thinking error.

Intelligence & Myside Processing

Toplak & Stanovich (2003) presented 112 undergraduate university students with an informal reasoning test in which they were asked to generate arguments both for and against the position they endorsed on three separate issues. Performance on the task was evaluated by comparing the number of arguments they generated which endorsed (myside arguments) and which refuted (otherside arguments) their own position on that issue. Participants generated more myside arguments than otherside arguments on all three issues, thus consistently showing a myside bias effect on each issue. Differences in cognitive ability were not associated with individual differences in myside bias. However, year in university was a significant predictor of myside bias. The degree of myside bias decreased systematically with year in university. Year in university remained a significant predictor of myside bias even when both cognitive ability and age were statistically partialled out.

Myside bias was displayed on all three issues, but there was no association in the level of myside bias shown across the different issues.

The researchers suggested that stronger myside bias is shown when issues are related to current beliefs:

[P]articipants showing a large myside bias on one issue did not necessarily display a large myside bias on the other two issues.

An explanation of this finding might be found in the concepts of the emerging science of memetics — the science of the epidemiology of idea-sized units called memes that are analogized to genes. Beliefs already stored in the brain are likely to form a structure that prevents contradictory beliefs from being stored (sometimes referred to over-assimilation).

Toplak and Stanovich suggested that, “it is not people who are characterized by more or less myside bias but beliefs that differ in the degree of belief bias they engender — that differ in how strongly they are structured to repel contradictory ideas.”

A negative correlation was found between year in school and myside bias. Lower myside bias scores were associated with length of time in university. This finding seems to suggest that higher education can meliorate rational thinking skills (at least some rational thinking skills) and lessens myside bias.

Stanovich and West (2007) conducted two experiments that investigated natural myside bias. In the two experiments involving a total of over 1,400 university students and eight different comparisons, very little evidence was found that participants of higher cognitive ability displayed less natural myside bias. Natural myside bias is the tendency to evaluate propositions in a biased manner when given no instructions to avoid doing so.

Macpherson and Stanovich (2007) examined the predictors of myside bias in two informal reasoning paradigms. The results showed cognitive ability did not predict myside bias. It was concluded that “cognitive ability displayed near zero correlations with myside bias as measured in two different paradigms.”

In Part Two, we look at more research and factors that contribute to myside bias.