Validation of the Normalized Difference Vegetation Index as a Measure of Neighborhood Greenness

PURPOSE: To assess the validity of a Geographic Information Systems (GIS) measure, the Normalized Difference Vegetation Index (NDVI), as a measure of neighborhood greenness for epidemiologic research. METHODS: Using remote-sensing spectral data, NDVI was calculated for a 100-m radial distance around 124 residences in greater Seattle. The criterion standard was rating of greenness for corresponding residential areas by 3 environmental psychologists. Pearson correlations and regression models were used to assess the association between the psychologists' ratings of greenness and NDVI. Analyses were also stratified by residential density to assess whether the correlations differed between low and high density. RESULTS: The mean NDVI among this sample of residences was 0.27 (standard deviation [SD], 0.11; range, 0.04 to 0.54), and the mean psychologist rating of greenness was 2.84 (SD, 0.98; range, 1-5). The correlation between NDVI and expert ratings of greenness was high (r = 0.69). The correlation was equivalently strong within each strata of residential density. CONCLUSIONS: NDVI is a useful measure of neighborhood greenness. In addition to showing a strong correlation with expert ratings, this measure has practical advantages, including availability of data and ease of application to various boundaries, which would aid in replication and comparability across studies. Ann Epidemiol 2011;21:946-952. (C) 2011 Elsevier Inc. All rights reserved.