Department stores need to close down shop at hundreds of locations across the country if they want to have any hope of regaining the levels of profitability they reached a decade ago, according to a new study by Green Street Advisors.

The real estate research firm says around 800 department stores must close—that’s nearly a fifth of all anchor space in US malls. And some retailers are harder hit than others—the study says Sears needs to close 300, or 43%, of its stores to regain the sales per square foot it had in 2006, the Wall Street Journal reports.

Many retailers seem to be heeding the advice, as chains like Macy's, Sears and Walgreens have seen a wave of closings in recent months, and others might be coming soon—Aeropostale just took the first steps down the store closing path.

But not all retailers are on board with the idea of massive store closings. JC Penney CFO Ed Records says it's a misconception that when a store closes its business transfers online, but rather online shopping suffers as stores disappear. [WSJ]