When there are multiple ways in which we are subject to risk, and we have the opportunity to reduce each category of risk, we are irrationally disposed to eliminate one category of risk. Some people will choose to do so even if choosing otherwise would reduce the total risk they face by more. One possible reason for this is that we sometimes think proportionally when we ought to be thinking quantitatively. Eliminating a category of risk represents a big difference in the proportion of that risk being eliminated, but a smaller difference in quantity. Another possible reason is that risks represent a cognitive strain. By eliminating one risk entirely, we reduce the amount of cognitive strain we face, making the option more appealing
In a study, subjects were told of two hazardous sites that caused a certain amount of cancer each year. They were given options of how many cases of cancer they could reduce. One option eliminated all cases from one site, while the other eliminate more total cases, but failed to eliminate all cases from either site. 42% of people chose the option that eliminated less total cases.