In the middle of March 2020, as the stock market collided with the pandemic and sank more than 30%, former hedge funder and DataTrek Research co-founder Nicholas Colas wrote that he had seen this before.

“So far, this is exactly October 2008,” he wrote at the time. With that in mind, DataTrek, an investment research firm, devoted a lot of its newsletter to the crisis playbook that involved buying the daily 5% drops when they came. Throughout, it proved to be an effective strategy — probably more effective than anyone would have thought — and the market returned to all-time highs by August.

Almost a year later and the similarities have not let up. In the firm’s newsletter this week, Colas pointed out that the "2009 playbook" is "still working even as we go deeper into 2021.”

Following the Financial Crisis, 219 days after the 2009 lows, the index was up 70%. Feb. 3 marked 219 trading days after the lows in March, and the S&P 500 was up 71%.

“Yes, we know. It’s creepy,” Colas wrote.

Even if the past is no guarantee of the future, DataTrek indulges the curiosity: if it’s been right so far, what about what’s next? It’s not great.

The chart is "flashing a warning sign," and if the correlation continues, a correction is coming. Back in 2010, the S&P 500 dropped 8.2%. But just a month later, the index was back to new all-time highs.

Colas and DataTrek are careful to note this is not a trading call. There is a lot of noise and other factors that can affect recoveries and market movements and even potential observation bias. That bias is interesting: Last spring, many investors expected the market would bounce back — albeit in the long run — and used the opportunity to buy the dip, according to brokerages. That buying helped counter the selloffs and helped the market recover.

Thinking about the comparison therefore is more instructive as a lesson about how cyclical recoveries work as time wears on, Colas wrote.

“The chart shows 2020 diverged from the 2009 path several times, and 2021 might well do the same,” he wrote. “But with so many market observers looking for a trading pullback, what we’re now calling the ‘2009–2010 Playbook’ offers productive guidance on what to expect and where to start buying.”

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Ethan Wolff-Mann is a writer at Yahoo Finance focusing on consumer issues, personal finance, retail, airlines, and more. Follow him on Twitter @ewolffmann.

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