title: Validation of a GIS facilities database: quantification and implications of error.
abstract: OBJECTIVE
  To validate a commercial database of community-level physical activity facilities that can be used in future research examining associations between access to physical activity facilities and individual-level physical activity and obesity.
  
  
  METHODS
  Physical activity facility characteristics and locations obtained from a commercial database were compared to a field census conducted in 80 census block groups within two U.S. communities. Agreement statistics, agreement of administratively defined neighborhoods, and distance between locations were used to quantify count, attribute, and positional error.
  
  
  RESULTS
  There was moderate agreement (concordance: nonurban: 0.39; urban: 0.46) of presence of any physical activity facility and poor to moderate agreement (kappa range: 0.14 to 0.76) of physical activity facility type. The mean Euclidean distance between commercial database versus field census locations was 757 and 35 m in the nonurban and urban communities, respectively. However, 94% and 100% of nonurban and urban physical activity facilities, respectively, fell into the same 5-digit ZIP code, dropping to 92% and 98% in the same block group and 71% along the same street.
  
  
  CONCLUSIONS
  Our findings suggest that the commercial database of physical activity facilities may contain appreciable error, but patterns of error suggest that built environment-health associations are likely biased downward.
authors.affiliation: Department of Nutrition, Schools of Public Health & Medicine, University of North Carolina at Chapel Hill, NC 27516-3997, USA.
authors.forename: Janne E
authors.initials: JE
authors.lastname: Boone
authors.forename: Penny
authors.initials: P
authors.lastname: Gordon-Larsen
authors.forename: James D
authors.initials: JD
authors.lastname: Stewart
authors.forename: Barry M
authors.initials: BM
authors.lastname: Popkin
mesh_terms: D016208:Databases, Factual; D004779:Environment Design; D020446:Fitness Centers / Q000600:supply & distribution*; D040362:Geographic Information Systems / Q000592:standards*; D015438:Health Behavior; D006801:Humans; D008377:Maps as Topic; D015203:Reproducibility of Results; D012111:Residence Characteristics / Q000706:statistics & numerical data*; D012680:Sensitivity and Specificity