Grades 6–8 · Organisms
How can an expectation shape the evidence we notice?
An expectation can guide attention toward useful information. It can also make supporting examples easier to notice than conflicting ones. Confirmation bias describes patterns in which searching for or interpreting evidence favors a belief we already hold.
In the diagramSelected examples are not the full recordAll six invented eveningsOnly successes selecteddonenot doneAll evenings included music; no comparison group is shownThe record is invented and establishes no effect of music on homework.
Imagine someone expects background music to improve homework. They remember a successful evening with music but overlook an unsuccessful one. If they only collect favorable evenings, the selected examples cannot fairly show whether music helped.
Even a remembered success can have other explanations: perhaps the assignment was easier or the person slept better. Evidence that fits a belief is not always evidence that distinguishes it from alternatives. Which observations were included matters as well as what they show.
Prior knowledge is not automatically a bias, and people do not always make this error. The concern is an uneven standard for evidence. Comparisons that include conflicting results and plausible alternatives can support a more dependable conclusion than a pile of selected successes.
About this explanation
Starting knowledge: Distinguish a proposed explanation from an observation and recognize that a result can fit more than one cause.
Sources
- Charlie Pilgrim and colleagues, Cognition — Confirmation bias emerges from an approximation to Bayesian reasoning