CREATE MEMBER CURRENTCUBE.[Measures].[Total_Patients_with_Medication]   
AS ( 
SUM( [Dim Medication].[Medication].[All].Children , [Measures].[# of Patients with Medication] )
) 
,  ASSOCIATED_MEASURE_GROUP = 'BB';    

-- to count Percent If NULL --> NULL
CREATE MEMBER CURRENTCUBE.[Measures].[% of Patients with Medication]   
AS 
(
 IIF ( [Measures].[Total_Patients_with_Medication] = NULL , NULL  , [Measures].[# of Patients with Medication]  / [Measures].[Total_Patients_with_Medication]   )
)  
,FORMAT_STRING = "Percent"
,  ASSOCIATED_MEASURE_GROUP = 'BB'