The one-year forward P/E ratio for the S&P 500 is 17.7, reports Factset. That’s the greatest level since 2004.

“The only time one-year multiples were higher in recent memory was during the tech craze of the late 1990s,” says Avery Shenfeld, chief economist at CIBC Capital Markets, in an economics report. “And that didn’t end well.”

Read: Energy and financials still most attractive in U.S.

He says higher valuations for U.S. equities reflect cost side, not growth. For instance, by 2018, the U.S. is expected to see lower corporate taxes and fewer regulations. The resulting savings would boost profits and share values.

But, “if it’s cost reductions in 2018 that the market is counting on stateside, the S&P would be vulnerable if there’s any political failure to deliver in the months ahead,” say Shenfeld and Nick Exarhos, director at CIBC Capital Markets, in the report.

In contrast, Dennis Mitchell, senior vice-president and senior portfolio manager at Sprott Asset Management, is optimistic for U.S. growth, as reported in a webinar on February 16 outlining his firm’s 2017 market outlook. That’s because OECD and IMF data have world growth at a solid 3.6% in 2018, thanks to an improved outlook for the U.S. economy.

Shenfeld considers how long the current expansion might last beyond 2017. “Some would argue the Obama expansion was already long in the tooth when Trump took office,” he says.

So far, we’re 92 months into this expansion. Since 1854, only one expansion — the one that started in 1991 — lasted significantly longer.

So, are North American equities ready for a correction?

Not necessarily, says Shenfeld. Expansions since 1945 have died out from either a severe oil shock or, more commonly, from a tightening cycle.

And those two things are unlikely, he says, given OPEC’s diminished market share as well as historical comparisons to where we are in the tightening cycle — a mere 50 bps off the lows in yields. At that same point in the most recent three cycles, the respective expansions still had more than six years left.

Mitchell expects any potential for multiple expansion to be confined to value equities. That’s because growth equities already trade at a higher multiple by definition, and, with greater growth expected, “those equities shouldn’t get the same bid as they have in the last six or seven years.”

Read: Why value investing is back in fashion

Shenfeld’s final thought: “Should equities cheapen up, it would represent a buying opportunity rather than the end of the cyclical run in the market,” says Shenfeld.

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