title: Comparing GIS-based measures in access to mammography and their validity in predicting neighborhood risk of late-stage breast cancer.
abstract: BACKGROUND
  Assessing neighborhood environment in access to mammography remains a challenge when investigating its contextual effect on breast cancer-related outcomes. Studies using different Geographic Information Systems (GIS)-based measures reported inconsistent findings.
  
  
  METHODS
  We compared GIS-based measures (travel time, service density, and a two-Step Floating Catchment Area method [2SFCA]) of access to FDA-accredited mammography facilities in terms of their Spearman correlation, agreement (Kappa) and spatial patterns. As an indicator of predictive validity, we examined their association with the odds of late-stage breast cancer using cancer registry data.
  
  
  RESULTS
  The accessibility measures indicated considerable variation in correlation, Kappa and spatial pattern. Measures using shortest travel time (or average) and service density showed low correlations, no agreement, and different spatial patterns. Both types of measures showed low correlations and little agreement with the 2SFCA measures. Of all measures, only the two measures using 6-timezone-weighted 2SFCA method were associated with increased odds of late-stage breast cancer (quick-distance-decay: odds ratio [OR] = 1.15, 95% confidence interval [CI] = 1.01-1.32; slow-distance-decay: OR = 1.19, 95% CI = 1.03-1.37) after controlling for demographics and neighborhood socioeconomic deprivation.
  
  
  CONCLUSIONS
  Various GIS-based measures of access to mammography facilities exist and are not identical in principle and their association with late-stage breast cancer risk. Only the two measures using the 2SFCA method with 6-timezone weighting were associated with increased odds of late-stage breast cancer. These measures incorporate both travel barriers and service competition. Studies may observe different results depending on the measure of accessibility used.
authors.affiliation: Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America. mlian@dom.wustl.edu
authors.forename: Min
authors.initials: M
authors.lastname: Lian
authors.forename: James
authors.initials: J
authors.lastname: Struthers
authors.forename: Mario
authors.initials: M
authors.lastname: Schootman
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis*; D005260:Female; D040362:Geographic Information Systems; D005843:Geography; D006297:Health Services Accessibility; D006801:Humans; D008327:Mammography / Q000379:methods*; D008875:Middle Aged; D015233:Models, Statistical; D016011:Normal Distribution; D025341:Principal Component Analysis; D012042:Registries; D012111:Residence Characteristics; D013997:Time Factors