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Are you getting any warnings in the log? For example, you might see WARNING: The bootstrap covariance is close to 0. WARNING: The ESTIMATE statement is ignored because the covariance could not be computed at QUANTILE= 0.5   These results make me think that a large proportion of your data is tied at the median value. Study the following example. In the example, the LOS_hours response variable is binned to the nearest hour and most of the values are tied values at the median. When the QUANTREG procedure estimates the median for each class, there is no variation. (Notice in your output that the standard error of each estimate is 0 and the confidence interval has zero length.)    I suggest you study (graph) your data to determine if your data are similar.  data Have; input trtgroup LOS_hours @@; datalines; 1 10 1 12 1 18 1 22 1 24 1 24 1 24 1 24 1 24 1 24 1 25 1 27 1 30 1 24 1 24 1 24 1 24 1 24 1 24 0 12 0 16 0 20 0 26 0 30 0 30 0 30 0 30 0 30 0 30 0 32 0 35 0 36 0 30 0 30 0 30 0 30 0 30 0 30 ; proc quantreg data=Have ci=resampling; class trtgroup; model LOS_hours = trtgroup/ quantile=0.5 ; estimate 'Diff in Medians' trtgroup 1 -1 / CL; run;   ... View more