The HPIMPUTE Procedure

PROC HPIMPUTE first computes the imputation value and then imputes with that value. Some statistics (such as the mean, minimum, and maximum) are computed precisely. The pseudo-median, which is calculated if you specify METHOD=PMEDIAN in the IMPUTE statement, is an estimation of the median. The computation of the median requires sorting the entire data. However, in a distributed computing environment, each grid node contains only a part of the entire data. Sorting all the data in such an environment requires a lot of internode communications, degrading the performance dramatically. To address this challenge, a binning-based method is used to estimate the pseudo-median. Experiments show that the pseudo-median is a good estimate of the median and that the performance is satisfactory.