Box-Jenkins(ARIMa) Models In an arima model. the random disturbance term E, is typically assumed to be"white noise;.e, it is identically and independently distributed with a mean of o and a common variance o across all observations e write d(0,a)5 Box-Jenkins (ARIMA) Models  In an ARIMA model, the random disturbance term is typically assumed to be “white noise”; i.e., it is identically and independently distributed with a mean of 0 and a common variance across all observations.  We write ~ i.i.d.(0, ) t  2  t  2 