Exploring three approaches for handling incomplete patient histories in a computer-based guideline for childhood immunization.

A significant problem faced by immunization registries is that the dates of a patient's previous vaccinations may not be known. These incomplete histories can pose a problem when attempting to use a computer-based guideline to produce patient-specific immunization recommendations automatically. This paper describes an overall approach- together with 3 specific strategies- developed to help deal with this problem. The paper then describes our experience applying the approach to a database containing over 400-000 immunization histories. The paper also discusses a number of the issues raised in adapting a computer-based guideline to accommodate incomplete patient data of this sort.