Thank you. That makes sense and seems to work. I created a measure as follows:
NonPayers = COUNT(MemberInfo[Code]) - DISTINCTCOUNT(Contributions[Code])
The problem now is how to plot this over months. It seems to take the NonPayers as a constant value. But I want to identify the number of NonPayers as a running total over months. So basically, I would like to plot the count of NonPayers over months--which should always be trending downward as new members make a payment. Thanks again.