ARCH Effects
ARCH effects refer to the presence of autoregressive conditional heteroskedasticity in a time series, which is the prerequisite for using GARCH models. These effects manifest as significant correlations in the squared residuals of a regression model.
If ARCH effects are present, it means that the variance of the errors is not constant but depends on the magnitude of past errors. Detecting these effects is the first step in volatility modeling, typically performed using tests like the Engle test.
In crypto markets, ARCH effects are almost always present due to the clustering nature of price returns. Identifying and confirming these effects justifies the use of advanced volatility models over simpler, homoskedastic approaches.
Without confirmed ARCH effects, the assumptions behind GARCH models would not hold, rendering the resulting volatility forecasts unreliable.