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Vanguard S&P 500 ETF GAS-GARCH Student T Volatility Analysis

Volatility prediction for Tuesday, October 20th, 2026

1 Day

12.07%

decreased by 0.55%

1 Week

12.34%

decreased by 0.28%

1 Month

13.21%

increased by 0.59%

Analysis last updated: Monday, October 19, 2026 at 09:57 PM UTC

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Date Range:

from

10/19/2024

to

10/19/2026

6M ·

1Y ·

2Y ·

5Y ·

10Y ·

All

graph of Vanguard S&P 500 ETF GAS-GARCH-T

News Impact Curve

How returns affect tomorrow's volatility

Volatility Forecast

How volatility evolves over time

Parameter Estimates

Sep 9, 2010 to Oct 16, 2026

Model Insight

Volatility shocks decay with a half-life of 26 trading days, meaning a shock loses half its impact after approximately 26 days. Returns follow a Student-t distribution with v = 6.76 degrees of freedom, capturing fatter tails than a normal distribution.

𝑓

GAS-GARCH-T Model

Tap to view equation

Shock decay: Shocks decay with a 26-day half-lifev = 6.76 · fat tails
ParamValuet-stat
ωconst1.0952
1.86*
αARCH0.1287
6.86***
βGARCH0.9742
62.08***
νDF6.7577
1.61

0.974

Persistence

26d

Half-life
𝑓

GAS-GARCH-T Model

Tap to view equation

ParameterValuet-statistic
ω

const

Unconditional variance weight

1.0952
1.86*
α

ARCH

Response to squared shocks

0.1287
6.86***
β

GARCH

Volatility persistence

0.9742
62.08***
ν

DF

Student-t tail thickness

6.7577
1.61

Persistence:

0.974

Half-life:

26 days