NEW YORK (Reuters) – The sharp rebound in equities has pushed widely used measures of valuing U.S. shares to their highest level in years.

Strategists say price-to-earnings ratios could go higher still given monetary stimulus, but huge uncertainty around earnings this year because of the economic fallout from the coronavirus makes for challenges in valuing shares.

Stock prices have risen even as earnings estimates have fallen, lifting multiples that were knocked down in the virus-driven market meltdown. The S&P 500 has recovered more than 25% from its March low following a raft of global stimulus and, more recently, after COVID-19 infections showed signs of peaking in parts of the United States.

The S&P 500’s P/E ratio, based on earnings estimates for the next four quarters, is now at 20.1, the highest in at least 15 years, according to IBES data from Refinitiv as of Friday. That’s up from about 14 just last month.

The forward P/E for Europe’s STOXX 600 is at 14.6, not far from the 15.3 level it reached on Feb. 26, and well above its recent low of 11.1 in March, based on Refinitiv’s data.

Meanwhile, analysts expect earnings for S&P 500 companies to drop 17.9% in 2020 from the previous year, the IBES data shows. That is much steeper than the 3.5% decline estimated at the start of the month.

“In certain cases, the valuations are not necessarily showing the true picture,” said Peter Cardillo, chief market economist at Spartan Capital Securities in New York.

First-quarter earnings for S&P 500 companies are expected to have declined 14.8% from the year-ago quarter, while second-quarter earnings are forecast to fall 33.3%.

Analysts’ earnings expectations could fall further, giving investors further reason to question current multiples.

Strategists see problems with European equity valuations as well.

“The P may be a little bit higher but not too stretched,” said Michael Bell, global market strategist at J.P. Morgan Asset Management. “It’s more that, it’s that the E is probably too optimistic.”

Referring to the current forward P/E for European equities, Goldman Sachs strategists wrote in a note: “If we think that the bottom-up consensus is too high, then this is pretty meaningless.”

Figuring out the extent to which the virus outbreak has hurt corporate profits has been difficult for analysts since many companies have been pulling guidance.

But the Federal Reserve’s stimulus could pave the way for even higher multiples.

“The Fed has picked up the mantle of ‘whatever it takes,’ and so has Congress,” said Quincy Krosby, chief market strategist at Prudential Financial in Newark, New Jersey. “So between monetary and fiscal policy, they have crossed into each other’s realms to help cushion the economy, so the economy can come back as quickly as possible.”