# Category aggregation

By default, Causal will take the

**sum**of each category item's value, to aggregate the variable. To change this, right-click on the variable and select a different**Category Aggregation**. For example, if you've split Bonus % input by Department, it might be more appropriate to see the average of the Departments, not the total.Other options are:

**None:**can be used when there is no meaningful way to aggregate a variable - it will just show a dash instead of any number. See None Values for more.**Min**and**Max:**takes the minimum or the maximum value of the category**Formula:**uses the variable's formula to calculate an aggregation value. Let's say you have a`Variable 1`

that uses the average and`Variable 2`

that uses the sum as the aggregations function. If you create a variable with the formula`Variable 1 + Variable 2`

and use the Formula aggregation, the aggregated value is the average of`Variable 1`

+ the sum of`Variable 2`

A good example of this is to think of gross margin across two different centres:- Profit Centre A - $100K in Net Sales, $90K in Costs - Gross margin is 10%
- Profit Centre B - $1M in Net sales, $500k in Costs - Gross margin is 50%

By default, Causal will display the Gross Margin variable (Net Sales-Revenue)/Net Sales as a “Sum” - so we would see 60% as our top-level Gross Margin. A common way around this is to use the “Average” category aggregation, which would display a 30% Gross Margin. This value is also incorrect, as Profit Centre B has much higher net-sales, and its impact to margin should be greater than Profit Centre A. Logically - the way to do this calculation appropriately would be to add the sales and costs of both profit centres, and then apply the calculation. This is what the “Formula” category aggregation helps us achieve, giving us the correct value of 46.4%