f1734adb_Dr__Arsham_s_Statistics_Site__The_Mode
[Fact No.] 6 [The Median] It is stable in that grouping procedures do not affect it appreciably. [The Mean] It may be calculated even when individual values are unknown, provided the sum of the values and the sample size n are known. [The Mode] 
It cannot be manipulated algebraically: modes of subgroups cannot be combined.
Dr. Arsham's Statistics Site
The Mode