The 3-day return spread between the S&P 500 and the equal-weight S&P 500 has fallen to one of the widest negative readings on record.

This means the S&P 500 index is surging while the average stock is being left behind.

For instance, last Friday's all-time high was driven almost entirely by Nvidia, Microsoft, and Amazon, with ONLY 36% of S&P 500 stocks closing higher on the day.

As a reminder, the equal-weight S&P 500 strips out the dominance of mega-cap stocks and gives every company the same weight, making it a cleaner measure of how the average stock is actually performing.

When the gap between the two is this wide, it signals that the rally is being driven by a handful of giants rather than broad market strength, a warning sign historically.

This is not a healthy market.