availability heuristic

The availability heuristic is a rule of thumb, heuristic, or cognitive bias, where people base their prediction of the frequency of an event or the proportion within a population based on how easily an example can be brought to mind. In these instances the ease of imagining an example or the vividness and emotional impact of that example becomes more credible than actual statistical probability. Because an example is easily brought to mind or mentally "available", the single example is considered as representative of the whole rather than as just a single example in a range of data. Several examples:Someone arrives late and says: "Sorry I'm late—I hit every red light on the way here." Here the aggravation of the red lights made them seem more prevalent than they actually were.Someone argues that cigarette smoking is not unhealthy because his grandfather smoked three packs of cigarettes a day and lived to be 100. The grandfather's health could simply be an unusual case that does not speak to the health of smokers in general.The president gives the State of the Union address and says that walnut farmers need a special farm subsidy. He points to a farmer in the balcony who is sitting next to his wife and explains how the farmer will benefit. Others who watch and discuss later agree that the subsidy is needed based on the benefit to that farmer. The farmer, however, might be the only person who will benefit from the subsidy. We don't know if walnut farmers in general need this subsidy.
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