With S&P 500 at record, is it still undervalued?

Traders work on the floor of the New York Stock Exchange.
Brendan McDermid | Reuters

With the S&P 500 and Nasdaq reaching all-time highs Monday, many investors continue to question the sustainability of the bull run, now in its 74th month (as in six years and two months).

Even though the market may be trading at a record, valuations show stocks are still attractive in relation to other asset classes, something that could lift equities even higher, according to Strategas Research.

In the past few years, the bears have been hit in the head over and over again as the market continued to climb to new highs, and even avoided a 10 percent correction along the way.

With the stocks hitting yet another milestone while earnings growth plateaus and the Federal Reserve threatens to raise interest rates, the bears came out in force this month with comparisons to the dot-com bubble and the overvaluation that ultimately ended that bull run in March 2000.

But Strategas found evidence to the contrary.

"The talk of a reprise of the tech bubble seems overblown," said Jason Trennert, the firm's chief investment strategist.