A graphical representation of sequential events in which the tree limbs designate human actions and other events as well as different conditions or influences upon these events. The values assigned to all tree limbs (except those in the first branching) are conditional probabilities. At any branch point in the tree, the sum of the probability values assigned to all of the limbs emanating from that point is 1.0. Typically the HRA event tree is drawn as a binary tree (i.e., only two limbs at each branch point).
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