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V-Lab

PSI 20 Portuguese Stock Index GAS-GARCH Student T Volatility Analysis

Volatility prediction for Wednesday, September 16th, 2026

1 Day

12.17%

increased by 0.25%

1 Week

12.33%

increased by 0.41%

1 Month

12.93%

increased by 1.01%

Analysis last updated: Tuesday, September 15, 2026 at 06:43 PM UTC

Date Range:

from

to

6M ·

1Y ·

2Y ·

5Y ·

10Y ·

All

graph of PSI 20 Portuguese Stock Index GAS-GARCH-T

News Impact Curve

How returns affect tomorrow's volatility

Volatility Forecast

How volatility evolves over time

Parameter Estimates

Dec 30, 1992 to Sep 11, 2026

Model Insight

With persistence 0.994, volatility shocks have a half-life of 124 trading days (~0.5 years), close to a unit root, so long-run forecasts are highly sensitive to this estimate. Returns follow a Student-t distribution with v = 6.73 degrees of freedom, capturing fatter tails than a normal distribution.

𝑓

GAS-GARCH-T Model

Tap to view equation

High persistence: persistence 0.994, shock half-life ~124 daysv = 6.73 · fat tails
ParamValuet-stat
ωconst1.9881
1.37
αARCH0.0959
14.88***
βGARCH0.9944
247.12***
νDF6.7318
3.14***

0.994

Persistence

124d

Half-life
𝑓

GAS-GARCH-T Model

Tap to view equation

ParameterValuet-statistic
ω

const

Unconditional variance weight

1.9881
1.37
α

ARCH

Response to squared shocks

0.0959
14.88***
β

GARCH

Volatility persistence

0.9944
247.12***
ν

DF

Student-t tail thickness

6.7318
3.14***

Persistence:

0.994

Half-life:

124 days