Rational ignorance

Rational ignorance is refraining from acquiring knowledge when the cost of educating oneself on an issue exceeds the potential benefit that the knowledge would provide.

Ignorance about an issue is said to be "rational" when the cost of educating oneself about the issue sufficiently to make an informed decision can outweigh any potential benefit one could reasonably expect to gain from that decision, and so it would be irrational to waste time doing so. This has consequences for the quality of decisions made by large numbers of people, such as general elections, where the probability of any one vote changing the outcome is very small.

The term is most often found in economics, particularly public choice theory, but also used in other disciplines which study rationality and choice, including philosophy (epistemology) and game theory.

The term was coined by Anthony Downs in An Economic Theory of Democracy.

Consider an employer attempting to choose between two candidates offering to complete a task at the cost of $10/hour. The length of time needed to complete the task may be longer or shorter depending on the skill of the person performing the task, so it is in the employer's best interests to find the fastest worker possible. Assume that the cost of another day of interviewing the candidates is $100. If the employer had deduced from the interviews so far that both candidates would complete the task in somewhere between 195 and 205 hours, it would be in the employer's best interests to choose one or the other by some easily applied metric (for example, flipping a coin) rather than spend the $100 on determining the better candidate, saving at most $100 in labor.

In many cases, the decision may be made on the basis of heuristics; a simple decision model which may not be completely accurate. For example, in deciding which brand of prepared food is most nutritious, a shopper might simply choose the one with (for example) the lowest amount of sugar, rather than conducting a research study of all the positive and negative factors in nutrition.

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