As the Nasdaq approached 5,000, many analysts said "this time is different."

The index crossed that mark on Monday for the first time since 2000, and there have been flashbacks to the crash that followed that peak when the dotcom bubble burst.

Some of these analysts argue that tech stock valuations are cheaper than they were then, and valuations are supported by strong earnings this time.

But according to Deutsche Bank, investors are missing a few key points about valuations:

From a note Friday:

There was much excitement about the milestone - with bulls and journalists seemingly unanimous that this time is different because today's 30 times price/earnings ratio [a measure of valuation] is miles from the bonkers 150 times seen at the end of the millennium. But current or forward earnings multiples are meaningless. If you smooth Nasdaq's volatile profits, and adjust for inflation, valuations look more worrying. Based on ten year average earnings the current PE is 50 times, versus 65 at the peak. More important, with the exception of QE-fuelled 2009, investors have been wise since 1999 to sell the Nasdaq whenever this so-called Shiller PE [another measure of valuation] reaches 50 times - with a subsequent average three year return of minus 20 percent.

The index was back near 4,000 in trading on Friday, falling with other major indices.

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