QUESTION:

What is an ARIMA model? Please explain in simple terms. No equations or math please. 

ANSWER:

In computing moving averages one needs to be concerned about two items:

1. The number of periods to be used ( i.e. the length of the weights or the number of weights )

and

2. The actual values of the weights. The answer to this double-edged question is called univariate

Box-Jenkins which if correctly implemented returns both the number of weights to be used and the actual

 coefficients to be applied to each lag. Modern approaches perform this task in a robust manner such that

 anomalies in the data be they

a. pulses b. level shifts c. seasonal pulses or d. time trends

are accounted for thus providing a "good model".

A productivity aid is available for this task is called AUTOBOX which rigorously examines the possible

 structures. This software even enables the in-line testing of constancy of variance and constancy of

 parameters. Univariate Box-Jenkins is also known as ARIMA and lots of material can be found at this

 website and other places in cyberspace. There is no need to ASSUME the number of weights and to

 ASSUME that all of the weights are equal.