# How to calculate statistical significance for Cost of Sales

#### FK11

##### New Member
Hi there, I work in ecommerce and we do a lot of AB testing.

I am testing 2 populations, and wanted to prove whether sample A has a significantly lower cost of sales vs. sample B

[note: cost of sales is calculated by cost / sales i.e. if you spend £20 and got £100 sales, then the cost of sales is 20/100 = 20%. The sample with a lower cost of sales wins]

What methodology should I use in order to calculate that?

Thanks!

#### noetsi

##### Fortran must die
If you are testing two populations, not samples, and population 1 has lower cost than sample b than it does. There is nothing to test statistically.

#### FK11

##### New Member
Hey thanks for the reply. Agree that if it is just pure cost we are looking then it doesn't require a test

However, what I want to see here is cost of sale. So the sales value is taken into account (i.e. Population A has a cost of sale of 20% vs. population B has a cost of sale of 10%). Any thought on how this can be tested?