The idea behind comps is to measure sales at “existing stores” and to net out sales from new stores. Generally, retailers calculate comps (or same-store sales) by taking the year-over-year % change in sales at stores open at least 1 year.

But the fact is that stores take several years (usually 3-5) to mature–and during those early years, they outperform the balance of the store base as awareness of the new stores steadily increases in the populations surrounding them. Once the reachable population is aware of astore, its growth rate falls to much lower levels.

So when retailers report comps, they’re really reporting sales for 2 out of 3 broad segments of their store base: mature stores (older than 5 years) and stores between 1 and 5 years old. Stores less than 1 year old are excluded.

It is not unusual for a retailer to report an increase in comps even as sales in its mature stores are declining. We agree that retailers should continue to report on at least a quarterly basis, but we advocate for more detailed reporting. Whole Foods is one of the few retailers that actually segments its store base by age and sets a strong example.

Here’s a link to a more detailed explanation, including some analysis of how Lowe’s, Walgreens’, Staples’, and other chains’ mature stores are performing.

http://www.retailnetgroup.com/Newsletter s/Files/RNGStrategyAlert-7.pdf