Forecasting the expected future range of the SPX by using current VIX : Example: VIX=25, then SPX over the next 30 days should swing inside a range of +/- 7.17% around current SPX spot (that's for a 1SD significance level, ie. in about 68% of observations). Here's the general formula (set z for different xSD): vix=25 ; z=1 ; dte=30 ; iv30 = vix / 100 * z * sqrt(dte / 365) * 100 ; iv30 7.17 Source: https://www.optiontradingtips.com/options101/volatility-option.html Alternatively one can use the ATM_IV_Avg of SPX options by taking the ATM IV avg of all ExpDates within the timeframe one wishes to forecast for. Yet another alternative is to use the HV of SPX. I think these latter 2 methods should be more accurate than the method using VIX, although VIX was intended exactly for this... And here's some interesting info about VIX by wikipedia : " On February 12, 2018, a letter was sent to the Commodity Futures Trading Commission and Securities and Exchange Commission by a law firm representing an anonymous whistleblower alleging manipulation of the VIX.[40] "
Here's a paper on SSRN[0] that suggests when the VIX has a standard deviation of 0.86 or below a spike is usually imminent. Doing a search for "VIX" on SSRN may surface some more useful info. [0] https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2949847
The vix relies on models created by banksters from Goldman Sachs. The SPX relies on models created by banksters from Standard and Poors. You can tell by the names of the firms that these two are different types of banksters and thus the two have no relation to eachother.