Frequencies for psi_90_safety_low_eststr variable in vwhqi_hosp_ahrq dataset :

PSI_90_SAFETY |
     _LOW_EST |      Freq.     Percent        Cum.
--------------+-----------------------------------
Not Available |      4,519      100.00      100.00
--------------+-----------------------------------
        Total |      4,519      100.00

by Jean Roth , jroth@nber.org , 16 Nov 2016