The study considers MA(1) model, because there are many processes that follow this structure. The model is a simple from of
Equation (8), and it represented as
The control limits for the MA(1) process is constructed as in Table II. The residuals term is given by the following formula:
2.2.3. ARMA model. The model is also a tool to understand and predict future values in the time series. It consists of two parts discussed in the previous subsection: AR and MA. The model is represented as ARMA(p, q) model where p is the order of the AR part, and q is the order of MA part, see Whitle.23 The model has general structure as follows