V-Lab
S&P 500 Equal Weight Index (EWI) GAS-GARCH Student T Volatility Analysis
Volatility prediction for Monday, September 21st, 2026
1 Day
11.99%
1 Week
12.13%
1 Month
12.65%
Analysis last updated: Saturday, September 19, 2026 at 12:03 AM UTC
News Impact Curve
How returns affect tomorrow's volatilityVolatility Forecast
How volatility evolves over timeParameter Estimates
Jan 1, 1990 to Sep 18, 2026Model Insight
With persistence 0.990, volatility shocks have a half-life of 69 trading days (~0.3 years), close to a unit root, so long-run forecasts are highly sensitive to this estimate. Returns follow a Student-t distribution with v = 8.48 degrees of freedom, capturing fatter tails than a normal distribution.
GAS-GARCH-T Model
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| Param | Value | t-stat |
|---|---|---|
| ωconst | 1.2605 | 1.84* |
| αARCH | 0.0845 | 10.10*** |
| βGARCH | 0.9901 | 166.84*** |
| νDF | 8.4849 | 1.48 |
0.990
Persistence69d
Half-lifeGAS-GARCH-T Model
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| Parameter | Value | t-statistic |
|---|---|---|
ω const Unconditional variance weight | 1.2605 | 1.84* |
α ARCH Response to squared shocks | 0.0845 | 10.10*** |
β GARCH Volatility persistence | 0.9901 | 166.84*** |
ν DF Student-t tail thickness | 8.4849 | 1.48 |
Persistence:
0.990
Half-life:
69 days
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