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Suppose we have the following linear trend model which holds for any time t:
Assuming that is independent zero-mean random noise, which of the following accurately represents the model at time , if the forecast is made at time ?
A
B
C
D
Explanation:
Explanation:
When forecasting at time for a future time , we need to consider:
Let's analyze each option:
Option A: Incorrect - Uses instead of and includes which should be omitted in a forecast
Option B: Incorrect - Uses instead of ; this would be forecasting based on current time rather than future time
Option C: Correct - Properly uses notation, includes , and correctly omits the error term since its expected value is zero
Option D: Incorrect - Includes which should not be in the forecast equation since we cannot know future error terms
The key insight is that in forecasting, we use the expected value of the model, and since , the error term drops out of the forecast equation.