There’s a few blogs out there which try to explain the problem and solutions. I looked at them and found that they were not always the easiest to wrap your head around. So, here is my solution which is hopefully a bit easier to understand and implement in your environment if needed.
The Business Problem: I want to calculate Month-over-Month (MoM) performance for online webinars
Approach: I know how many attendees attended webinars in a given month and therefore to work out the delta between Month 1 and Month 2 is simple subtraction. The problem is that the monthly attendee value is calculated by a COUNTROW function, surfaced by its own measure (Session Attendees). So, how do I keep this dynamic with the minimum amount of formulas?
1. Create a new measure to show the Previous Month value:
PreviousMonthMeasure = CALCULATE([SessionAttendeesMeasure],PARALLELPERIOD(SessionDate,-1,MONTH
2. Create a measure to calculate the delta:
MoMDeltaMeasure = SessionAttendeesMeasure – PreviousMonthMeasure
3. To calculate the delta percentage, create a final measure
MoMPerformanceMeasure = MoMDeltaMeasure/PreviousMonthMeasure
(make sure you set this in the modeling as a percentage value)
In summary, your table should look something like this:
|Performance +/- MoM