The S & P 500's 14-day relative strength index, or RSI, closed above 81 on Wednesday.
This coincided with the S & P 500 closing above 5,600 for the first time.
The S & P 500 has closed with an RSI above 81 only 12 other times in the past 40 years, Cantor head of equity derivatives Eric Johnston pointed out.
After entering such overbought conditions, the S & P 500 has averaged a decline of 2.21% in the following 15 days, Johnston's data shows.
Traders took some profits off the table on Thursday, with the S & P 500 losing 0.9%, pulling back from the all-time highs reached in the previous session.
Persons:
Cantor Fitzgerald, Cantor, Eric Johnston
Organizations:
Traders