A small area index of gentrification, applied to New York City

This paper presents a small-area index of the multifactorial phenomenon loosely referred to as gentrification, with application to New York City (NYC). The relative change of key input variables (median family income, median rent and proportions of non-Hispanic white, 20-34-year-olds and adults with a 4-year college degree) was computed from the years 2000 to 2016 for NYC census tracts that are spatially normalized to the year 2010. Raw scores derived from principal components analysis were then spatially smoothed through a fully Bayesian conditional autoregressive model, presenting an innovation over previous methods since it essentially blurs the otherwise artificial tract boundaries and results in a simulated posterior distribution of scores for each tract. The median and upper/lower percentiles provide a point estimate and assessment of uncertainty, respectively, of gentrification for each tract. The mapped index is visually consistent with the general understanding of gentrification in NYC, and the index is positively associated with census tract-level change in home values, as measured separately from a real property database. Although we developed this index as the quantitative part of a mixed methods approach to understanding gentrification in New York City, the methodology is intended to be applicable in other cities.