title: Using network projections to explore co-incidence and context in large clinical datasets: Application to homelessness among U.S. Veterans.
abstract: Network projections of data can provide an efficient format for data exploration of co-incidence in large clinical datasets. We present and explore the utility of a network projection approach to finding patterns in health care data that could be exploited to prevent homelessness among U.S. Veterans.
  
  
  
  We divided Veteran ICD-9-CM (ICD9) data into two time periods (0-59 and 60-364days prior to the first evidence of homelessness) and then used Pajek social network analysis software to visualize these data as three different networks. A multi-relational network simultaneously displayed the magnitude of ties between the most frequent ICD9 pairings. A new association network visualized ICD9 pairings that greatly increased or decreased. A signed, subtraction network visualized the presence, absence, and magnitude difference between ICD9 associations by time period.
  
  
  
  A cohort of 9468 U.S. Veterans was identified as having administrative evidence of homelessness and visits in both time periods. They were seen in 222,599 outpatient visits that generated 484,339 ICD9 codes (average of 11.4 (range 1-23) visits and 2.2 (range 1-60) ICD9 codes per visit). Using the three network projection methods, we were able to show distinct differences in the pattern of co-morbidities in the two time periods. In the more distant time period preceding homelessness, the network was dominated by routine health maintenance visits and physical ailment diagnoses. In the 59days immediately prior to the homelessness identification, alcohol related diagnoses along with economic circumstances such as unemployment, legal circumstances, along with housing instability were noted.
  
  
  
  Network visualizations of large clinical datasets traditionally treated as tabular and difficult to manipulate reveal rich, previously hidden connections between data variables related to homelessness. A key feature is the ability to visualize changes in variables with temporality and in proximity to the event of interest. These visualizations lend support to cognitive tasks such as exploration of large clinical datasets as a prelude to hypothesis generation.
authors.affiliation: IDEAS Center, VA Salt Lake City Health Care System, Salt Lake City, UT, United States; Department of Internal Medicine, University of Utah, Salt Lake City, UT, United States.
authors.forename: Warren B P
authors.initials: WB
authors.lastname: Pettey
authors.affiliation: IDEAS Center, VA Salt Lake City Health Care System, Salt Lake City, UT, United States; Department of Internal Medicine, University of Utah, Salt Lake City, UT, United States; Department Mathematics, University of Utah, Salt Lake City, UT, United States.
authors.forename: Damon J A
authors.initials: DJ
authors.lastname: Toth
authors.affiliation: IDEAS Center, VA Salt Lake City Health Care System, Salt Lake City, UT, United States; Department of Internal Medicine, University of Utah, Salt Lake City, UT, United States.
authors.forename: Andrew
authors.initials: A
authors.lastname: Redd
authors.affiliation: IDEAS Center, VA Salt Lake City Health Care System, Salt Lake City, UT, United States; Department of Internal Medicine, University of Utah, Salt Lake City, UT, United States.
authors.forename: Marjorie E
authors.initials: ME
authors.lastname: Carter
authors.affiliation: IDEAS Center, VA Salt Lake City Health Care System, Salt Lake City, UT, United States; Department of Internal Medicine, University of Utah, Salt Lake City, UT, United States; Department Biomedical Informatics, University of Utah, Salt Lake City, UT, United States.
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Samore
authors.affiliation: IDEAS Center, VA Salt Lake City Health Care System, Salt Lake City, UT, United States; Department of Internal Medicine, University of Utah, Salt Lake City, UT, United States; Department Biomedical Informatics, University of Utah, Salt Lake City, UT, United States. Electronic address: adi.gundlapalli@hsc.utah.edu.
authors.forename: Adi V
authors.initials: AV
authors.lastname: Gundlapalli
mesh_terms: D000328:Adult; D000368:Aged; D019058:Community Networks; D003626:Data Display; D005260:Female; D005544:Forecasting; D006703:Ill-Housed Persons; D006801:Humans; D015994:Incidence; D038801:International Classification of Diseases; D008297:Male; D008875:Middle Aged; D012944:Social Support; D014728:Veterans
keywords: Data exploration; Homelessness; ICD9 codes; Information foraging; Social network analysis; U.S. Veterans