2 Replies Latest reply on Jan 4, 2019 10:51 AM by Scott Henry

    Average of percentages, unweighted

    Scott Henry

      Hello -


      My goal is to understand how to average of unweighted percentages, instead of aggregating values before calculating. I need to see the average of percent difference without considering the weight of the percentages.


      My scenario: what is the average percent tuition price drop among my selected colleges? What is the average enrollment change for those colleges?


      My problem: the aggregation of the values prior to calculating the percent change weights percentages, where I want them unweighted, which seems counter intuitive to Tableau.


      Example: College A costs $10k and has 2,000 students in year 0; in year 1 they decrease cost to $8k and have 3,000 students. So, cost -25% and enrollment +50%. College B  costs $20k and has 10,000 students in year 0; in year 1 they decrease cost to $18k and have 9,000 students, so cost -10% and enrollment -10%. I want to see that the overall average cost change among colleges was 17.5%, and overall enrollment change was +20%.


      Of course, Tableau is going to tell me that average decrease was 13.3%, and the enrollment didn't change at all 0.0%. Because those values are aggregated, then averaged, that way they are weighted comparatively. Which is all true. But not the question I'm trying to answer!


      I want to aggregate all the percentages, THEN take the average of those percentages, NOT the overall average of the aggregates! It's driving me crazy. Please help?


      In the workbook, I would expect the 'Grand Total' for year 0 to be 2.83%, NOT -1.1%. Thanks for the ideas!