Inter-patient distance metrics using SNOMED CT defining relationships.
BACKGROUND
Patient-based similarity metrics are important case-based reasoning tools which may assist with research and patient care applications. Ontology and information content principles may be potentially helpful tools for similarity metric development.


METHODS
Patient cases from 1989 through 2003 from the Columbia University Medical Center data repository were converted to SNOMED CT concepts. Five metrics were implemented: (1) percent disagreement with data as an unstructured "bag of findings," (2) average links between concepts, (3) links weighted by information content with descendants, (4) links weighted by information content with term prevalence, and (5) path distance using descendants weighted by information content with descendants. Three physicians served as gold standard for 30 cases.


RESULTS
Expert inter-rater reliability was 0.91, with rank correlations between 0.61 and 0.81, representing upper-bound performance. Expert performance compared to metrics resulted in correlations of 0.27, 0.29, 0.30, 0.30, and 0.30, respectively. Using SNOMED axis Clinical Findings alone increased correlation to 0.37.


CONCLUSIONS
Ontology principles and information content provide useful information for similarity metrics but currently fall short of expert performance.
Department of Surgery, The Johns Hopkins Medical Institutions, Baltimore, MD, USA. gmelton@jhmi.edu <gmelton@jhmi.edu>
Genevieve B
GB
Melton
Simon
S
Parsons
Frances P
FP
Morrison
Adam S
AS
Rothschild
Marianthi
M
Markatou
George
G
Hripcsak
D000465:Algorithms; D015510:Clinical Medicine / Q000145:classification*; D006801:Humans; D016247:Information Storage and Retrieval; D016347:Medical Records Systems, Computerized / Q000145:classification*; D015233:Models, Statistical; D008962:Models, Theoretical; D009323:Natural Language Processing; D039061:Systematized Nomenclature of Medicine; D018511:Systems Integration; D009626:Terminology as Topic; D017432:Unified Medical Language System; D018875:Vocabulary, Controlled