title: A systematic evaluation of different methods for calculating adolescent vaccination levels using immunization information system data.
abstract: OBJECTIVE
  Immunization information systems (IISs) are valuable surveillance tools; however, population relocation may introduce bias when determining immunization coverage. We explored alternative methods for estimating the vaccine-eligible population when calculating adolescent immunization levels using a statewide IIS.
  
  
  METHODS
  We performed a retrospective analysis of the Michigan State Care Improvement Registry (MCIR) for all adolescents aged 11-18 years registered in the MCIR as of October 2010. We explored four methods for determining denominators: (1) including all adolescents with MCIR records, (2) excluding adolescents with out-of-state residence, (3) further excluding those without MCIR activity ≥ 10 years prior to the evaluation date, and (4) using a denominator based on U.S. Census data. We estimated state- and county-specific coverage levels for four adolescent vaccines.
  
  
  RESULTS
  We found a 20% difference in estimated vaccination coverage between the most inclusive and restrictive denominator populations. Although there was some variability among the four methods in vaccination at the state level (2%-11%), greater variation occurred at the county level (up to 21%). This variation was substantial enough to potentially impact public health assessments of immunization programs. Generally, vaccines with higher coverage levels had greater absolute variation, as did counties with smaller populations.
  
  
  CONCLUSIONS
  At the county level, using the four denominator calculation methods resulted in substantial differences in estimated adolescent immunization rates that were less apparent when aggregated at the state level. Further research is needed to ascertain the most appropriate method for estimating vaccine coverage levels using IIS data.
authors.affiliation: University of Michigan, Department of Pediatrics, Child Health Evaluation and Research Unit, Ann Arbor, MI.
authors.forename: Charitha
authors.initials: C
authors.lastname: Gowda
authors.forename: Shiming
authors.initials: S
authors.lastname: Dong
authors.forename: Rachel C
authors.initials: RC
authors.lastname: Potter
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Dombkowski
authors.forename: Shannon
authors.initials: S
authors.lastname: Stokley
authors.forename: Amanda F
authors.initials: AF
authors.lastname: Dempsey
mesh_terms: D000293:Adolescent; D019352:Censuses; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines; D006801:Humans; D017589:Immunization Programs / Q000706:statistics & numerical data*; D007252:Influenza Vaccines; D007256:Information Systems / Q000706:statistics & numerical data; D022401:Meningococcal Vaccines; D008824:Michigan; D015588:Observer Variation; D053918:Papillomavirus Vaccines; D011159:Population Surveillance / Q000379:methods*; D012042:Registries; D012189:Retrospective Studies; D014611:Vaccination / Q000706:statistics & numerical data*
chemical_list: D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines; D007252:Influenza Vaccines; D022401:Meningococcal Vaccines; D053918:Papillomavirus Vaccines