The city's transportation system, and the population density it makes possible, also have other effects. Scientists at Columbia University examined data from 13,102 adults in the city's five boroughs and identified correlations between New York's built environment and public health. New Yorkers residing in densely populated, pedestrian-friendly areas have significantly lower body mass index (BMI) levels compared to other New Yorkers. Three characteristics of the city environment—living in areas with mixed residential and commercial uses, living near bus and subway stops and living in population-dense areas—were found to be inversely associated with BMI levels.