Mean Period Change Excl Current = 
VAR _CurrentPeriod = SELECTEDVALUE ( <<DateTable>>[<<DateColumn>>] )
VAR _ChangesForContext = 
    FILTER (
        ADDCOLUMNS ( ALL ( <<DateTable>>[<<DateColumn>>] ), "@Change", [Period Change] ),
        NOT ISBLANK ( [@Change] ) && <<DateTable>>[<<DateColumn>>] <> _CurrentPeriod
    )
RETURN AVERAGEX ( _ChangesForContext, [@Change] )
 

StdDev Period Change Excl Current = 
VAR _CurrentPeriod = SELECTEDVALUE ( <<DateTable>>[<<DateColumn>>] )
VAR _ChangesForContext = 
  FILTER (
        ADDCOLUMNS ( ALL ( <<DateTable>>[<<DateColumn>>] ), "@Change", [Period Change] ),
        NOT ISBLANK ( [@Change] ) && <<DateTable>>[<<DateColumn>>] <> _CurrentPeriod
    )
RETURN STDEVX.S ( _ChangesForContext, [@Change] )