V-Lab
S&P 500 Index APARCH Volatility Analysis
Volatility prediction for Wednesday, September 23rd, 2026
1 Day
11.53%
1 Week
11.87%
1 Month
13.05%
Analysis last updated: Wednesday, September 23, 2026 at 12:31 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
This asset exhibits a strong leverage effect: volatility responds almost entirely to negative shocks. The ARCH response to positive shocks is negligible. The volatility power δ = 1.05 sits below 2, so large shocks influence volatility less than quadratically, a more outlier-robust response than standard GARCH.
APARCH Model
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| Param | Value | t-stat |
|---|---|---|
| ωconst | 0.0287 | 9.12*** |
| αARCH | 0.0845 | 7.88*** |
| βGARCH | 0.9065 | 101.94*** |
| γleverage | 0.9000 | 5.37*** |
| δpower | 1.0476 | 10.49*** |
0.976
Persistence28d
Half-lifeAPARCH Model
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| Parameter | Value | t-statistic |
|---|---|---|
ω const Unconditional variance weight | 0.0287 | 9.12*** |
α ARCH Response to squared shocks | 0.0845 | 7.88*** |
β GARCH Volatility persistence | 0.9065 | 101.94*** |
γ leverage Additional response to negative shocks | 0.9000 | 5.37*** |
δ power Transformation power | 1.0476 | 10.49*** |
Persistence:
0.976
Half-life:
28 days
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