Can the Cboe Correlation Index Predict VIX Spikes?

The Cboe Correlation Index, ticker COR1M, sounds complicated, but the idea behind it is simple. It measures how much the 500 stocks inside the S&P 500 are expected to move together. A high reading means investors expect the whole market to rise and fall as one herd. A low reading means they expect stocks to drift in their own directions. We lined up its reading for every trading day since October 2021, about 1,140 days, against the S&P 500 itself and the VIX, to answer one plain question: does it actually tell you anything useful?

The short answer, in one table

Below is a summary of COR1M’s key relationships. The first two are strong, while the last two show almost no meaningful connection.

COR1M Relationship	Strength	What It Means
S&P 500 (same day)	Strong	Moves inversely: COR1M rises when the market falls
VIX (same day)	Very Strong	Moves in tandem with the VIX
S&P 500 (next day)	Almost None	No meaningful predictive power for the next day
Future volatility spike	No Reliable Link	Historical testing shows no consistent relationship

It rises when the market falls

On any given day, COR1M and the S&P 500 move in opposite directions. When the index jumps, the market is usually having a red day. When it drops, the market is usually green. Here is the average S&P 500 move, split by which way COR1M went that day:

On days COR1M	The S&P 500 averaged
went up	−0.45%
went down	+0.48%

It is a strong, dependable same-day relationship, and it makes sense. When stocks fall, they tend to fall together, so correlation rises. When they climb calmly, they spread out, so correlation drops.

It is almost a copy of the VIX

If COR1M moves with fear, how does it compare to the market’s best-known fear gauge, the VIX? They are close to identical. For the past few years the two have risen and fallen almost in step. Hover the chart to see both on any date:

They move together about 80 percent of the time. So if you already keep an eye on the VIX, COR1M is mostly telling you the same story in different clothing.

But it cannot tell you what happens next

Everything above is about today. The moment you ask COR1M to predict tomorrow, it goes quiet. The bars below show how reliably it is connected to each thing, on a scale of 0 (no link) to 100 (perfect lockstep). Hover any bar to read it. Its link to the next day’s market move is almost exactly zero:

Here is that zero in real numbers. The same-day link is strong: when COR1M rose, the market was down that day, and when COR1M fell, the market was up. But the next day, that link is gone:

On days COR1M	S&P 500 that day	S&P 500 the next day
went up	−0.45%	+0.06%
went down	+0.48%	+0.04%

Whether COR1M jumped or dropped today, the next day averaged about the same small gain, roughly +0.05%, no different from any random day. A move that is strong today carries no information into tomorrow.

A popular idea is that an unusually calm market, when COR1M sits very low, sets up a sudden volatility spike. We checked how often the VIX actually jumped 10 points or more after COR1M sat in its lowest 10 percent, against a typical day:

When COR1M was	VIX jumped 10+ pts within 1 week	within 2 weeks
in its lowest 10% (the calmest)	4.6%	7.3%
on a typical day	2.3%	5.1%

So there is a mild lean. At its calmest, a 10-point VIX jump was about twice as likely over the next week as on a typical day. But the raw odds stay small, around 7 percent over two weeks, so it points to slightly higher risk rather than a clear warning. Two things keep it weak: the bump shows up only at the rare, very lowest readings (COR1M merely in its lower quarter showed no jump), and those extreme-calm stretches have clustered in the last two years, so it has not been tested across many different markets.