title: Optimized probability sampling of study sites to improve generalizability in a multisite intervention trial.
abstract: BACKGROUND
  Studies of type 2 translation, the adaption of evidence-based interventions to real-world settings, should include representative study sites and staff to improve external validity. Sites for such studies are, however, often selected by convenience sampling, which limits generalizability. We used an optimized probability sampling protocol to select an unbiased, representative sample of study sites to prepare for a randomized trial of a weight loss intervention.
  
  
  METHODS
  We invited North Carolina health departments within 200 miles of the research center to participate (N = 81). Of the 43 health departments that were eligible, 30 were interested in participating. To select a representative and feasible sample of 6 health departments that met inclusion criteria, we generated all combinations of 6 from the 30 health departments that were eligible and interested. From the subset of combinations that met inclusion criteria, we selected 1 at random.
  
  
  RESULTS
  Of 593,775 possible combinations of 6 counties, 15,177 (3%) met inclusion criteria. Sites in the selected subset were similar to all eligible sites in terms of health department characteristics and county demographics.
  
  
  CONCLUSIONS
  Optimized probability sampling improved generalizability by ensuring an unbiased and representative sample of study sites.
authors.affiliation: University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Kraschnewski
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Keyserling
authors.forename: Shrikant I
authors.initials: SI
authors.lastname: Bangdiwala
authors.forename: Ziya
authors.initials: Z
authors.lastname: Gizlice
authors.forename: Beverly A
authors.initials: BA
authors.lastname: Garcia
authors.forename: Larry F
authors.initials: LF
authors.lastname: Johnston
authors.forename: Alison
authors.initials: A
authors.lastname: Gustafson
authors.forename: Lindsay
authors.initials: L
authors.lastname: Petrovic
authors.forename: Russell E
authors.initials: RE
authors.lastname: Glasgow
authors.forename: Carmen D
authors.initials: CD
authors.lastname: Samuel-Hodge
mesh_terms: D000328:Adult; D005260:Female; D006077:Government Agencies; D006282:Health Personnel; D006296:Health Services / Q000706:statistics & numerical data; D006302:Health Services Research / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D008875:Middle Aged; D009657:North Carolina / Q000453:epidemiology; D050177:Overweight / Q000453:epidemiology / Q000628:therapy; D011203:Poverty; D012494:Sampling Studies; D013219:State Government; D015431:Weight Loss