I have the following timeseries with a frequency of 12 (months). Since there is both a trend and seasonality, I differenced the timeseries. To determine the parameters p, q, P and Q for the SARIMA(p, 1, q)(P, 1, Q)_12 model, I look at the ACF and PACF of the differenced timeseries, shown below.
Now how do I determine the values for p, q, P and Q? I am having trouble reading the ACF and PACF. My guess is parameter P is 0 because the PACF does not show spikes at lag 24 and parameter Q is 2 because the ACF shows 2 spikes after lag 0, 12 and 24. Am I correct so far? About parameters p and q I am clueless.
As a note:
auto.arima() gives a SARIMA(1,1,2)(0,1,2)_12 model.