These are the counts produced by cty_sub.cc:
     
     total = 95412
     total_sub = 5000
     yes = 4843
     yes_sub = 943
     no = 4057
     no_sub = 4057
     freq = 0.0507588
     freq_sub = 0.1886
     OSR = 3.71561

The size of the raw data set is 95412 of which 5000 were randomly
sampled for cty_sub.dat.

The proportion of donors in the raw data set is 5.07588%.

The proportion of donors in the subset is 18.86%.

This is an over sampling rate of 0.1886/0.0507588 = 3.71561.