Figure 4. Representative schematic of a segment typing tool.

For individual targeting, field workers or other stakeholders can use typing tools that quickly identify which segment an individual most likely belongs to. Splits in a decision tree-based typing tool can be based on categorical or continuous variables alike, and are chosen by the algorithm to identify members of each segment as accurately as possible. By giving responses to each question, a person is then allocated to a segment at the end of their path. Here, we show a hypothetical example of what a typing tool could look like to allocate a parent into existing segments relating to child vaccination behaviors. A parent in a given segment might be more or less likely to vaccinate their child, for different reasons. The field worker can then select an intervention or message that is most likely to resonate with that specific segment. For practicality, typing tools often stick to the three or four most predictive questions. However, that practicality has a tradeoff with typing accuracy: the more accurate a typing tool needs to be, the more questions must be asked.