State Street SPDR S&P 500 ETF Trust GAS-GARCH Student T Volatility Analysis
Volatility prediction for Tuesday, October 20th, 2026
1 Day
11.62%
decreased by 0.33%
1 Week
11.81%
decreased by 0.14%
1 Month
12.49%
increased by 0.54%
Analysis last updated: Monday, October 19, 2026 at 09:55 PM UTC
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News Impact Curve
How returns affect tomorrow's volatilityVolatility Forecast
How volatility evolves over timeParameter Estimates
Jan 29, 1993 to Oct 16, 2026Model Insight
Volatility shocks decay with a half-life of 62 trading days, meaning a shock loses half its impact after approximately 62 days. Returns follow a Student-t distribution with v = 6.82 degrees of freedom, capturing fatter tails than a normal distribution.
𝑓
GAS-GARCH-T Model
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Shock decay: Shocks decay with a 62-day half-lifev = 6.82 · fat tails
| Param | Value | t-stat |
|---|---|---|
| ωconst | 1.3408 | 1.68* |
| αARCH | 0.0921 | 10.29*** |
| βGARCH | 0.9889 | 139.30*** |
| νDF | 6.8242 | 2.20** |
0.989
Persistence62d
Half-life𝑓
GAS-GARCH-T Model
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| Parameter | Value | t-statistic |
|---|---|---|
ω const Unconditional variance weight | 1.3408 | 1.68* |
α ARCH Response to squared shocks | 0.0921 | 10.29*** |
β GARCH Volatility persistence | 0.9889 | 139.30*** |
ν DF Student-t tail thickness | 6.8242 | 2.20** |
Persistence:
0.989
Half-life:
62 days
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