The correct formula uses RUNNING_SUM to accumulate sales by category in order, then divides by the total sales using TOTAL to get the cumulative percentage. This is essential for Pareto analysis to show the cumulative contribution.
The classic Pareto chart combines bars sorted by descending value with a line showing cumulative percentage. This helps identify the vital few categories contributing most of the sales.
Having all relevant dimensions and measures in one data source allows Tableau to calculate cumulative sales correctly across combined categories and regions for Pareto analysis.
RUNNING_SUM(SUM([Sales])) / SUM([Sales])
The denominator SUM([Sales]) returns the sales for the current row only, not the total sales. For cumulative percentage, the denominator must be the total sales across all rows, which requires TOTAL(SUM([Sales])).
The Pareto principle states that a small percentage of causes (categories) often account for a large percentage of effects (sales). This insight helps prioritize business efforts on the vital few.