Fault trees: Sensitivity of estimated failure probabilities to problem representation.

: Fault trees represent problem situations by organizing things that could go wrong into functional categories. Such trees are essential devices for analyzing and evaluating the fallibility of complex systems. They follow many different formats, sometimes by design, other times inadvertently. Major results were: people were quite insensitive to what had been left out of a fault tree, increasing the amount of detail for the tree as a whole or just for some of its branches produced small effects on perceptions, and the perceived importance of a particular branch was increased by presenting it in pieces (as two separate component branches). Aside from their relevance for the study of problem solving, such results may have important implications for how best to inform the public about technological risks and to involve it in policy decisions and how experts should perform fault-tree analyses of the risks from technological systems.