In reply to ljc.

That formula does not provide an estimate for a quantile. It estimates the empirical distribution function for the data. If you want to estimate the empirical distribution function (ECDF) in SAS, you can use PROC UNIVARIATE:

proc univariate data=Have;
cdfplot x / vscale=proportion;
ods output cdfplot=outCDF; /* data set contains ECDF values */
run;