Do you think making a seasonal adjustment will be useful, given what you observe at this point?

Run four regressions:

1. seasonally unadjusted monthly as the dependent, and tt and t2t2 as the independents,
2. seasonally unadjusted monthly as the dependent, and tt, t2t2, and DD as the independents,
3. seasonally adjusted monthly as the dependent, and tt and t2t2 as the independents, and
4. seasonally adjusted monthly as the dependent, and tt, t2t2, and DD as the independents.

In interpreting your p-values, remember that, say, 1.0E-08 is 1.010?81.010?8, which is 0.00000001

In comparing the regression results between models 1 and 2 (the unadjusted sales), it is notable that including the extra variable DD in model 2?

In comparing the regression results between models 2 and 3, it is notable that?

The regression results for model 4 are notable because?