In a world narrowly defined by the S&P 500, only five names matter and Apple Inc. is not one of them.

Amazon.com Inc. AMZN, -4.12% , Alphabet Inc. GOOGL, -3.45% , Microsoft Corp. MSFT, -3.29% , Facebook Inc. FB, -2.24% , and General Electric Co. GE, -2.24% combined are responsible for more than 100% of the large-cap index’s return this year, underscoring the narrow breadth of the market, according to Goldman Sachs.

“Our index has experienced only 11 narrow breadth periods since 1985, including three during the late 1990s that share several characteristics with the current narrow breadth episode,” said David Kostin, chief U.S. equity strategist at Goldman Sachs, in his weekly report.

Goldman Sachs’ breadth index is calculated by assigning each S&P 500 SPX, -2.37% constituent with weights and six-month returns to calculate market breadth on a scale of 0 to 100. The index is currently at 1, among the lowest in 30 years.

“The Breadth index has stayed below 5 for at least two consecutive months just 11 times since 1985,” Kostin noted.

Goldman Sachs

A typical narrow breadth cycle — when a few stocks drive the market — lasts four months and so-called mega-cap stocks with strong balance sheets tend to outperform the broader index. The current phase is only one month old and is likely to persist into early 2016, he said.

While Kostin stressed that narrow breadth is not necessarily a signal for a recession, he also noted the similarities between the current trend and the tail end of the tech bubble in the late 1990s, in particular the forward price-to-earnings ratio.

“S&P 500 forward price to earnings currently equals 16.3x, near the highest level since the tech bubble,” said Kostin.

In sum, if these five stocks were out of the picture, the S&P 500’s return year to date would have been 2.2% lower. The five stocks together account for roughly 9% of the S&P 500’s market cap.

List of top stocks contributing to S&P 500 total return

Goldman Sachs

Apple AAPL, -4.19% , a stock with almost cult status given its popularity with investors, contributed 20% to the S&P 500’s total return for 2015, compared with 114% from Amazon, according to Goldman Sachs.

As of Monday, Apple shares are up 2.4% year to date and are off 16% from their 52-week high of $134.54 on April 28.