Tech stocks are flashing a warning sign similar to before the dot-com bubble popped

A measure comparing riskier tech stocks to safer utilities is triggering memories of what happened just before the dotcom bubble wrecked the market 18 years ago.

Price performance between the two sectors has spread lately to a gap not quite as wide as during the bubble, but close. Using a measure called the "Popular/Panned Ratio", Jim Paulsen, chief investment strategist at the Leuthold Group, sees danger signs growing for the bull market that began nine years ago.

"Even though its magnitude is less dramatic, the character of the PP Ratio in this bull market is amazingly similar to what occurred during the 1990s," Paulsen said in a note to clients. "The obsession with dot-com stocks in the late-1990s has been replaced today by a fascination with FANG stocks." FANG stocks entail Facebook, Amazon, Netflix and Google-parent Alphabet.

While the performance gap between the two sectors stayed flat during the early years of the bull run, it has expanded since 2016 and has surged in recent months.

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