Frequencies for first 10,000 rows of stratm variable in nhamcsopd1995 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      5,542       55.42       55.42
        202 |      3,709       37.09       92.51
        203 |        584        5.84       98.35
        204 |        165        1.65      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016