st: about centile and r(c_#)

["G. Dai" <dgecon@gmail.com>]

hi all,

I'm lit bit confused by centile. for example
************************
.clear
.sysuse auto

. centile price, c(30   60)

                                                       -- Binom. Interp. --
    Variable |     Obs  Percentile      Centile        [95% Conf. Interval]
-------------+-------------------------------------------------------------
       price |      74         30        4424.5        4110.565    4679.134
             |                 60          5705        4912.708    6232.007

*************************

then I want to know the values of centiles, say

*****************************
. di r(c_30)
*****************************
I get missing values.

while

**************************
. di $S_7
4424.5
**********************

so, why r(c_30) doesn't work and why $S_7 works?

thanks,

Guang
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