Statement as per the book official GARP book (chapter 11, seasonal differencing):
How is this equation MA(1)? Isnt this an MA(4) with theta=-1?
And how is this covariance stationary? The characteristic equation is 1+z^4 with complex root of abs value of unity.
Learning outcomes: Describe the properties of the first-order moving average (MA(1)) process, and distinguish between autoregressive representation and moving average representation. Describe the properties of a general finite-order process of order q (MA(q)) process