Estimated OLS of SPX to VIX
Below is a daily SPX to VIX chart (black dots) with SPX (green line) and VIX (below price chart), since 1990. The gray line is the estimated OLS (ordinary least squares or best fitting line) from 1990 to 2000 (over a structural bull market period). The OLS of the SPX to VIX ratio is upward sloping, because over time SPX will rise, while VIX will trade in a range.
The chart shows the SPX to VIX ratio is at the furthest distance above the OLS line since at least 1990. Also, the steep slope and extended rise, since July, has been the greatest since at least 1990. So, the ratio indicates SPX is severely overbought and there may be little upside short-term. Also, there may be a substantial pullback intermediate-term.