title: Incorporating the Last Four Digits of Social Security Numbers Substantially Improves Linking Patient Data from De-identified Hospital Claims Databases.
abstract: OBJECTIVE
  Assess algorithms for linking patients across de-identified databases without compromising confidentiality.
  
  
  METHODS
  Hospital discharges from 11 Mayo Clinic hospitals during January 2008-September 2012 (assessment and validation data). Minnesota death certificates and hospital discharges from 2009 to 2012 for entire state (application data).
  
  
  METHODS
  Cross-sectional assessment of sensitivity and positive predictive value (PPV) for four linking algorithms tested by identifying readmissions and posthospital mortality on the assessment data with application to statewide data.
  
  
  METHODS
  De-identified claims included patient gender, birthdate, and zip code. Assessment records were matched with institutional sources containing unique identifiers and the last four digits of Social Security number (SSNL4).
  
  
  RESULTS
  Gender, birthdate, and five-digit zip code identified readmissions with a sensitivity of 98.0 percent and a PPV of 97.7 percent and identified postdischarge mortality with 84.4 percent sensitivity and 98.9 percent PPV. Inclusion of SSNL4 produced nearly perfect identification of readmissions and deaths. When applied statewide, regions bordering states with unavailable hospital discharge data had lower rates.
  
  
  CONCLUSIONS
  Addition of SSNL4 to administrative data, accompanied by appropriate data use and data release policies, can enable trusted repositories to link data with nearly perfect accuracy without compromising patient confidentiality. States maintaining centralized de-identified databases should add SSNL4 to data specifications.
authors.affiliation: Mayo Clinic, Rochester, MN.
authors.forename: James M
authors.initials: JM
authors.lastname: Naessens
authors.affiliation: Mayo Clinic, Robert D. and Patricia E. Kern Center for the Science of Healthcare Delivery, Rochester, MN.
authors.forename: Sue L
authors.initials: SL
authors.lastname: Visscher
authors.affiliation: Mayo Clinic, Robert D. and Patricia E. Kern Center for the Science of Healthcare Delivery, Rochester, MN.
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Peterson
authors.affiliation: Mayo Clinic, Robert D. and Patricia E. Kern Center for the Science of Healthcare Delivery, Rochester, MN.
authors.forename: Kristi M
authors.initials: KM
authors.lastname: Swanson
authors.affiliation: Mayo Clinic, Robert D. and Patricia E. Kern Center for the Science of Healthcare Delivery, Rochester, MN.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Johnson
authors.affiliation: Mayo Clinic, Robert D. and Patricia E. Kern Center for the Science of Healthcare Delivery, Rochester, MN.
authors.forename: Parvez A
authors.initials: PA
authors.lastname: Rahman
authors.affiliation: Minnesota Hospital Association, St Paul, MN.
authors.forename: Joe
authors.initials: J
authors.lastname: Schindler
authors.affiliation: Minnesota Hospital Association, St Paul, MN.
authors.forename: Mark
authors.initials: M
authors.lastname: Sonneborn
authors.affiliation: Michael Pine Associates, Chicago, IL.
authors.forename: Donald E
authors.initials: DE
authors.lastname: Fry
authors.affiliation: Michael Pine Associates, Chicago, IL.
authors.forename: Michael
authors.initials: M
authors.lastname: Pine
mesh_terms: D000465:Algorithms; D003430:Cross-Sectional Studies; D003625:Data Collection / Q000379:methods; D016208:Databases, Factual; D003644:Death Certificates; D005006:Ethnicity / Q000706:statistics & numerical data*; D006302:Health Services Research / Q000458:organization & administration*; D006801:Humans; D008498:Medical Record Linkage; D008910:Minnesota / Q000453:epidemiology; D009026:Mortality / Q000639:trends*; D010351:Patient Discharge; D010359:Patient Readmission / Q000706:statistics & numerical data; D058996:Quality Improvement; D044469:Racial Groups / Q000706:statistics & numerical data*; D012680:Sensitivity and Specificity; D012943:Social Security / Q000706:statistics & numerical data*
keywords: Readmission; de-identified data; posthospital mortality; record linkage