title: Arima formula in R
body: <p>I am using "Arima" to build a MA(1) model for "Airpassengers", the code is bellow:</p>
  
  <pre><code> test3=Arima(AirPassengers,c(0,0,1))
  </code></pre>
  
  <p>The result is</p>
  
  <pre><code>Series: AirPassengers 
  ARIMA(0,0,1)            with non-zero mean 
  
  Coefficients:
           ma1      mean
        0.9642  280.6464
  s.e.  0.0214   10.5788
  
  sigma^2 estimated as 4265:  log likelihood=-806.43
  AIC=1618.86   AICc=1619.03   BIC=1627.77
  </code></pre>
  
  <p>I wonder for the final formula, which one is correct :</p>
  
  <p>(1) Yt=280.6464+et+0.9642et-1</p>
  
  <p>(2) Yt=280.6464+et-0.9642et-1</p>