Neighboring tobacco retailers may share similarities (i.e., spatial autocorrelation may be present), causing the collected data to violate assumptions of independence in standard statistical tests.31 Of the 5 articles53-55,63,64 that reported intraclass correlations for measures of marketing, the intraclass correlations ranged from 0.025 for retailers' number of smokeless tobacco ads in census block groups in a Midwestern US city63 to 0.36 for the proportion of menthol marketing at retailers in census tracts in St. Louis, Missouri.55 Eight studies addressed this issue by using mixed models, usually multilevel models or generalized estimating equations.26,41,43,53-55,61,72 Another 4 studies corrected for dependence using robust SEs.32,63,64,67 One article aggregated marketing to the census tract (index value per square mile) and found no significant spatial autocorrelation as indicated by Moran's I and Geary's c.59 However, the majority of research (70%) did not comment on the issue of spatial autocorrelation. What does this mean in simpler terms