title: Application of a new method for linking anonymous survey data in a population of soldiers returning from Iraq.
abstract: OBJECTIVE
  This study provides a unique application of a procedure to link anonymous survey records as a means to assess mental health problems among soldiers after return from deployment to Iraq. The research purpose is to validate the use of a linkage method on anonymous survey data for longitudinal analysis.
  
  
  METHODS
  This research analyzes surveys completed by soldiers at three (N = 4,903), six (N = 3,110), and 12 (N = 2,544) months post-Operation Iraqi Freedom (OIF) deployment. To protect anonymity while also allowing for longitudinal analysis, the survey includes four self-generated codes for matching the surveys from individual soldiers. The surveys were linked using Link Plus (Centers for Disease Control and Prevention, Atlanta, GA). Three matched groups (3-6 months, 6-12 months, and 3-12 months) were created, matching on the anonymous codes and demographic variables. An internal validation of the linkage results was performed and selection bias was assessed.
  
  
  RESULTS
  The matched records showed very high agreement in variables not included in the matching procedure and were similar to the unmatched records with regard to demographics and post-traumatic stress disorder (PTSD) prevalence.
  
  
  CONCLUSIONS
  The use of self-generated codes protects anonymity while the method utilized and validated in this paper allows for longitudinal data analysis. The results support an absence of any notable selection bias.
authors.affiliation: George Washington University, Washington, DC, USA. abigail.wilson@gmail.com
authors.forename: Abigail L
authors.initials: AL
authors.lastname: Garvey Wilson
authors.forename: Charles W
authors.initials: CW
authors.lastname: Hoge
authors.forename: Dennis
authors.initials: D
authors.lastname: McGurk
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Thomas
authors.forename: Julie C
authors.initials: JC
authors.lastname: Clark
authors.forename: Carl A
authors.initials: CA
authors.lastname: Castro
mesh_terms: D000293:Adolescent; D000328:Adult; D055826:Afghan Campaign 2001-; D000465:Algorithms; D002487:Centers for Disease Control and Prevention, U.S.; D003130:Combat Disorders / Q000453:epidemiology; D003625:Data Collection / Q000379:methods* / Q000592:standards*; D004812:Epidemiologic Methods; D005260:Female; D006306:Health Surveys / Q000379:methods*; D006801:Humans; D007493:Iraq; D008137:Longitudinal Studies; D008297:Male; D008498:Medical Record Linkage / Q000379:methods / Q000592:standards; D008875:Middle Aged; D008889:Military Personnel / Q000523:psychology; D057566:Self Report; D013313:Stress Disorders, Post-Traumatic / Q000453:epidemiology; D014342:Truth Disclosure; D014481:United States / Q000453:epidemiology; D055815:Young Adult