Optimal hierarchy as a means of increasing the flexibility of a morbidity classification system.

Established systems of problem or morbidity classification do not always meet special needs for higher levels of specificity in coding. Optional hierarchy is a mechanism that may be employed to achieve the desired specificity for local use while permitting recombination into parent rubrics for external comparisons. Optional hierarchy may be employed to develop subdivision rubrics when justified by the high incidence of specific problems, whether due to geographic or social circumstances or because of the special nature of individual practice(s). It may also be used to meet the sometimes esoteric needs of the researcher, the unique needs of the teacher, or the preferential needs of other individual recorders. While the development of subdivision rubrics is simple, care is required to avoid pitfalls in reversion to the parent rubric. Failure to ensure the accuracy of this reversion can destroy a fundamental purpose of morbidity classification--the intercenter comparison of data. Although this paper discusses the application of optional hierarchy to the International Classification of Health Problems in Primary Care (ICHPPC), it is equally useful in other systems of classification.