Proximity.zip is a zip file with the data set and programs used in D. Card "Using Geographic Variation in College Proximity to Estimate the Return to Schooling" The zip file contains 3 files (plus this readme file): -- a codebook -- a data set -- an example sas program to read the data and process it. The code book "code_bk.txt" gives the variables in the data set and their means and min/max values. It also gives a reference for the article by D. Card that the data is derived from. The data set is nls.dat = ascii file of data, 3613 obs Finally, there a sas program, read1.sas , a program that reads the nls.dat file and runs an example regression. The varibles are named and explained in the file.