Frequencies for first 10,000 rows of exp_dt_num variable in drug2009q4 dataset :

 Expiration |
date of the |
      drug. |
 (YYYYMMDD) |      Freq.     Percent        Cum.
------------+-----------------------------------
  31jan2009 |          1        0.01        0.01
  31may2009 |          1        0.01        0.02
  01sep2009 |          1        0.01        0.03
  01oct2009 |          1        0.01        0.04
  01jan2010 |          1        0.01        0.05
  28feb2010 |          1        0.01        0.06
  01mar2010 |          1        0.01        0.07
  31mar2010 |          1        0.01        0.08
  01apr2010 |          1        0.01        0.09
  01sep2010 |          1        0.01        0.10
  30sep2010 |          4        0.04        0.14
  01dec2010 |          1        0.01        0.15
  01feb2011 |          1        0.01        0.16
  28feb2011 |          1        0.01        0.17
  31mar2011 |          1        0.01        0.18
  30apr2011 |          1        0.01        0.19
  01oct2011 |          1        0.01        0.20
  01dec2011 |          1        0.01        0.21
  31jan2012 |          1        0.01        0.22
  01feb2013 |          1        0.01        0.23
  28feb2014 |          1        0.01        0.24
          . |      9,976       99.76      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 18 Dec 2015