A time series representing the total monthly electricity generated in the United States

(in millions of kilowatt-hours) for the period January 1970 to December 2005 is available as series ‘electricity’ in the R TSA package.

(a) Plot the series and comment. Is a variance stabilizing transformation needed for this case?

(b) Determine a suitable model for the series following the iterative three-stage procedure of model identification, parameter estimation, and diagnostics checking.

(c) Is there evidence of a deterministic seasonal pattern in this series? If so, how would this impact your choice of model for this series?