Frequencies for po_box variable in hcris2552_96_2011 dataset :

     po_box |      Freq.     Percent        Cum.
------------+-----------------------------------
            |         30       88.24       88.24
       1269 |          1        2.94       91.18
        186 |          1        2.94       94.12
        240 |          1        2.94       97.06
        392 |          1        2.94      100.00
------------+-----------------------------------
      Total |         34      100.00

by Jean Roth , jroth@nber.org , 2 Sep 2018