Introduction to tree diagrams

Tree diagrams in benefit-risk assessments are called value trees. Value trees are a visual, hierarchical depiction of key ideas, values, or concepts used in decision, through an explicit visual map of the attributes or criteria of decisions that are of value to the decision-makers. The value tree is a particularly useful tool because it requires decision-makers to clarify which benefits and risks are pivotal to the benefit¨Crisk balance, and its visual nature greatly enhances communication. The tree diagram can be presented to the general public through mass media, patients, physicians, regulators and other experts.

Value trees differ from decision trees; the latter are tools used to map and weight choice options. The application ofa decision treemay only be limited to expert audiences.

The value tree in isolation does not provide sufficient information about the context within which it is created, and does not convey why certain criteria are chosen whilst others are not. However, a value tree is borne out of a specific context which should be made available with the visualisation. The tree elicits questions and facilitates a more open benefit-risk discussion around the selection or non-selection of criteria. Value trees also do not indicate any correlation between criteria.Since tree diagrams do not typically present quantitative data, it is possible for individuals to misinterpret the number of criteria in a quantitative manner, that is, if the number of risks is greater than the number of benefits, the benefit-risk balance must be negative.

Almost any decision analysis support tools such as Hiview 3, IDS, V.I.S.A, Web-HIPRE, Microsoft Word® and Microsoft Excel® can create tree diagrams. One of the software packages dedicated to creating tree diagram is FreeMind, which also has built-in features that allow the tree diagram to be used interactively by expanding and collapsing the branches from a parent node as well as allowing additional text annotations to be added to the nodes.