Auditing complex concepts of SNOMED using a refined hierarchical abstraction network

Abstract

Auditors of a large terminology, such as SNOMED CT, face a daunting challenge. To aid them in their efforts, it is essential to devise techniques that can automatically identify concepts warranting special attention. "Complex" concepts, which by their very nature are more difficult to model, fall neatly into this category. A special kind of grouping, called a partial-area, is utilized in the characterization of complex concepts. In particular, the complex concepts that are the focus of this work are those appearing in intersections of multiple partial-areas and are thus referred to as overlapping concepts. In a companion paper, an automatic methodology for identifying and partitioning the entire collection of overlapping concepts into disjoint, singly-rooted groups, that are more manageable to work with and comprehend, has been presented. The partitioning methodology formed the foundation for the development of an abstraction network for the overlapping concepts called a disjoint partial-area taxonomy. This new disjoint partial-area taxonomy offers a collection of semantically uniform partial-areas and is exploited herein as the basis for a novel auditing methodology. The review of the overlapping concepts is done in a top-down order within semantically uniform groups. These groups are themselves reviewed in a top-down order, which proceeds from the less complex to the more complex overlapping concepts. The results of applying the methodology to SNOMED's Specimen hierarchy are presented. Hypotheses regarding error ratios for overlapping concepts and between different kinds of overlapping concepts are formulated. Two phases of auditing the Specimen hierarchy for two releases of SNOMED are reported on. With the use of the double bootstrap and Fisher's exact test (two-tailed), the auditing of concepts and especially roots of overlapping partial-areas is shown to yield a statistically significant higher proportion of errors.

Figure 1

The concept Dialysis fluid specimen belongs to the partial-areas rooted at Fluid sample and Drug specimen, as indicated by the color coding. It is therefore an example of an overlapping concept

Figure 2

The 15 overlapping roots from the area {substance} of the Specimen hierarchy (July 2009) are shown as multi-colored boxes among other concepts. The coloring indicates their ancestry

Figure 3

The portion of the disjoint partial-area taxonomy for the area {substance} corresponding to the concept network in Figure 2 (SNOMED 2009)

Figure 4

An indented display of four d-partial-areas and their constituent concepts illustrating the topological-sort-order processing

Figure 5

Flow diagram summarizing the audits of SNOMED 2007 and 2009. The numbers in each box represent the respective numbers from the 2007 and 2009 versions of SNOMED. For example, “1,056/1,236” in the top box indicates that there are 1,056 concepts in the Specimen hierarchy in SNOMED 2007 and 1,236 in 2009

Figure 6

A portion of the disjoint partial-area taxonomy for the area {substance} (July 2007). The multi-colored boxes are the d-partial-areas containing overlapping concepts

Figure 7

Area taxonomy for SNOMED’s Specimen hierarchy (July 2009). The boxes are the areas, and the lines are the child-of relationships

Figure 8

Partial-area taxonomy for the Specimen hierarchy (July 2009). The main boxes are the areas, and the lines are the child-of relationships. The embedded boxes are the partial-areas