I am trying to choose the correct ARIMA model. To get a stationary series on which to plot the ACF and PACF on I've done the following transformations on my original series:
- natural log
- 1st non-seasonal differences
- 1st seasonal differences of the non-seasonal differences
Judging from my time series plot(included below) the final series seems stationary but unfortunately I can't interpret the ACF plot. It looks to me like it would need further or different transformations.
This is my data set with the transformations I've done.
I included my plots below. I am using minitab 18 to generate these.