Hello, I dont understand how schweser came up with the answer for the question below. Based on my reading to adjust for seasonality you add a lag ofthe dependent variable to the model. Couldnt A also be an answer? Give me your take on this Thanks ________________________________________________________________________ Which of the following is a seasonally adjusted model? A) Salest = b0 + b1 Sales t-1 + b2 Sales t-2 + åt. B) Salest = b1 Sales t-1+ åt. C) (Salest - Sales t-1)= b0 + b1 (Sales t-1 - Sales t-2) + b2 (Sales t-4 - Sales t-5) + åt. Your answer: A was incorrect. The correct answer was C) (Salest - Sales t-1)= b0 + b1 (Sales t-1 - Sales t-2) + b2 (Sales t-4 - Sales t-5) + åt. This model is a seasonal AR with first differencing.