When a comparative histogram is generated in PROC UNIVARIATE by using the CLASS and HISTOGRAM statements, and the MAXSIGMAS= or MAXNBIN= option is specified on the HISTOGRAM statement, histogram bins will be incorrect in any non-key cell having data that fall below the leftmost bin in the key cell.

If SAS/QC is available, the problem can be circumvented by using the COMPHISTOGRAM statement in PROC CAPABILITY. In PROC UNIVARIATE, the MAXSIGMAS= or MAXNBIN= option must be removed in order to avoid the problem.