According to the information from the non-official news app Zhitongcaijing, last week, as large tech stocks rose, while other stocks in the market lagged behind, the performance gap between the S&P 500 index and its equally weighted stocks reached a significant new extreme.

According to market data from Dow Jones, for the first time since 1990, the performance of the traditional market-cap weighted S&P 500 index has exceeded that of the S&P 500 equal weight index by 2 percentage points or more for two consecutive weeks.

However, this is not the only milestone that suggests a growing divergence between these two indices. Analysts use these two indices as a rough standard to measure market breadth.

According to Jonathan Krinsky, chief market technician at BTIG, based on data since 1990, the relative strength index of the S&P 500 index exceeded 70 on Thursday, while the RSI of the S&P equal weight index fell below 50 for the first time. This situation occurred again on Friday.

Krinsky explained that there is a big gap between these two momentum indicators. RSI is a momentum indicator used by many technical analysts, with a reading over 70 indicating that an index or security is overbought, while a reading below 50 indicates it is oversold.

These two indicators seem to be moving in different directions, the latest sign of the degree of market differentiation in the US.

In addition, the proportion of S&P 500 index members trading above their 50-day moving average has dropped to below 50%, while the index itself continues to trade above its mid-term average line, up more than 4%.

Krinsky pointed out that this is a situation that has not been seen since the months leading up to the bursting of the tech bubble in December 1999. The "poor breadth" of the US stock market has been a widely discussed topic among professional investors for most of the past year.

But last week, analysts' discussions about the narrowing market gains seemed to reach a fever pitch. Many cited various indicators to illustrate the new extremes of differentiation under the surface of the S&P 500 index, as only a few stocks, mainly Nvidia (NVDA.US) and Apple (AAPL.US), have risen recently. According to FactSet data, the S&P 500 index hit historic highs on four of the five trading days last week.

An analyst team from Bespoke Investment Group emphasized on Monday that the S&P 500 index no longer seems to reflect the performance of its ordinary member stocks.

The cumulative rise and fall of the index last year failed to set a new high along with this year's index. Instead, the gap between the number of individual stocks rising and falling with the S&P 500 index has actually continued to widen. Last week, the number of stocks in the S&P 500 index that hit new lows in 52 weeks was higher than the number that hit new highs in 52 weeks.

Finally, although the S&P 500 index remains firmly in overbought territory, the overbought level of the S&P 500 index technology sector is even higher. Hence, the gap between the 50-day moving average of the two has reached its widest level since last year.

However, even within the technology sector, the recent large fluctuations have worsened, indicating that the influence of a few super large-cap stocks is becoming greater. Recently, less than 65% of the companies in the sector have seen their stock prices rise above their 50-day moving average, far below the level at the beginning of this year.