Autoregressive Moving Average Model (ARMA) = calculates an average value over a period of time to smooth fluctuations in a time series.
ARMA models are very sensitive to minor changes and may rarely forecast well.
Auto Regressive Conditional Heteroskedasticity (ARCH) testing = can be used to determine if an AR, MA, or ARMA model suffers from conditional heteroskedasticity.
The ARCH test models the error terms and if its slope is statistically significant, then the predictive AR, MA, or ARMA model under scrutiny is not valid.
