For each product that matches the criteria, the most recent recorded price for each chain is calculated, and then the average of those prices is taken. For each chain, the best price is compared to the average, and then we take the average of the averages. For the missing products, we guess what the price would have been by taking the average price of that product across other chains and then applying the average-average formula on it. We use averages because they help to offset the distortion caused by incorrect prices entered into the system.

We end up with an adjusted total for each chain, which is a combination of the actual prices and the estimated prices for the missing products. We then order the chains by that adjusted total.

These results fail to account for differentiated pricing, where some stores within a chain might have a different markup, depending on their location. For instance, rural stores with higher distribution costs might have higher prices, which could push up the total for the chain. Additionally, these results don't include the advantages gained from loyalty schemes.

• Matched Products - The number of products in the basket for which there is a recorded price for this chain
• Total on Matches - The total of the most recent prices for all the matched products
• Dif to Avg - The percentage difference compared to the average price across all the chains listed
• Adjusted Total - Using the average difference, the total basket is estimated as though the chain stocked every time
• Dif to Best - The difference between the chain's adjusted total and the best total available