Comment:

Point based outcomes for all four sections of Philadelphia combined. The paper also provides results for each of the four sections separately. We specified cross-sectional time-series linear regression models in which the units of observation were number of vacant lots (i) per year of the study (t) and in which the difference-in-differences term, Pit 3 Rit, was our focal independent variable, defined as the interaction between a pregreening-postgreening difference per vacant lot, Pit, where pregreening years were 0 and postgreening years were 1, and a treatment-control difference, Rit, where control lots were 0 and greened lots were 1. The b3 coefficient for the difference in differences term is intended to estimate the true effect of the treatment on the outcome (41). Each of our regression models also included a different health or safety outcome of interest.