MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 25: MDX Grammar

Leveling Rules for MDX Numeric Value Function

The following numeric functions are optional: MEDIAN, VAR, STDEV, RANK, AGGREGATE, COVARIANCE, CORRELATION, LINREGINTERCEPT, LINREGSLOPE, LINREGVARIANCE, LINREGR2, and LINREGPOINT. Consumers can check the value of the property MDPROP_MDX_NUMERIC_FUNCTIONS to see whether a provider supports this feature.