The Common Data Elements for cancer research: remarks on functions and structure

Abstract

Objectives: The National Cancer Institute (NCI) has developed the Common Data Elements (CDE) to serve as a controlled vocabulary of data descriptors for cancer research, to facilitate data interchange and inter-operability between cancer research centers. We evaluated CDE's structure to see whether it could represent the elements necessary to support its intended purpose, and whether it could prevent errors and inconsistencies from being accidentally introduced. We also performed automated checks for certain types of content errors that provided a rough measure of curation quality.

Methods: Evaluation was performed on CDE content downloaded via the NCI's CDE Browser, and transformed into relational database form. Evaluation was performed under three categories: 1) compatibility with the ISO/IEC 11179 metadata model, on which CDE structure is based, 2) features necessary for controlled vocabulary support, and 3) support for a stated NCI goal, set up of data collection forms for cancer research.

Results: Various limitations were identified both with respect to content (inconsistency, insufficient definition of elements, redundancy) as well as structure--particularly the need for term and relationship support, as well as the need for metadata supporting the explicit representation of electronic forms that utilize sets of common data elements.

Conclusions: While there are numerous positive aspects to the CDE effort, there is considerable opportunity for improvement. Our recommendations include review of existing content by diverse experts in the cancer community; integration with the NCI thesaurus to take advantage of the latter's links to nationally used controlled vocabularies, and various schema enhancements required for electronic form support.

Figure 1

A Unified Modeling Language (UML) Class Diagram describing CDE content. The key classes tables from the perspective of element use are Concepts, Value Domains, Data Elements and Choices. The classes are implemented as relational tables: in each class, the symbols ≪PK≫ and ≪FK≫ indicate primary and foreign keys, respectively.

Fig. 2

Details of an individual Common Data Element (the summary result of an abdominal CT scan to assess disease). The Value Domain and Concept that this CDE.belongs to are shown on the top right, while the individual Choices in the value domain and the various Classification categories that apply to this element are shown in lists on the lower part of the screen. Note that the names of the Value Domain and the Concept associated with the Data Element are highly similar to that of the element itself (using the string “ABDOMINAL_CT_RESULT”), indicating that they have possibly been algorithmically generated. This follows the requirements that every data element must be associated with a concept as well as a domain: both of these must be created accordingly if they did not exist in the database previously.