How to analyse individual products


I'm trying to figure out the best way of analysing a product's performance within the constrains of the site's performance.

If I imagine the following example of three different stores selling three identical products:

Store / Store Performance
A 150%
B 100%
C 50%

Product Breakdown Percentage
Store / Chocolate / Drinks / Sweets
A 50% 30% 20%
B 60% 20% 20%
C 70% 20% 10%

If I want to analyse the performance of the products then my initial thought would be to make a weighted performance average (store performance x product breakdown x number of products). This gives me weighted product performances of Chocolate 170%, Drinks 75% and Sweets 55%.

However, it doesn't feel correct to present these results as I'm declaring a single product as outperforming the whole store. On the flip side though, if I cap chocolate at the store's performance, the product sum is now less than the store average.

I hope I've explained clearly enough my issue. Can anyone point me in the right direction of the accepted way to analyse this situation?
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