The Acf Is Clearly Declining Very Slowly in This Case

question 5

Multiple Choice

The acf is clearly declining very slowly in this case, which is consistent with their being an autoregressive part to the appropriate model. The pacf is clearly significant for lags one and two, but the question is does it them become insignificant for lags 2 and 4, indicating an AR(2) process, or does it remain significant, which would be more consistent with a mixed ARMA process? Well, given the huge size of the sample that gave rise to this acf and pacf, even a pacf value of 0.001 would still be statistically significant. Thus an ARMA process is the most likely candidate, although note that it would not be possible to tell from the acf and pacf which model from the ARMA family was more appropriate. The DGP for the data that generated this plot was y_t = 0.9 y_(t-1) - 0.3 u_(t-1) + u_t.
-Consider the following AR(2) model. What is the optimal 2-step ahead forecast for y if all information available is up to and including time t, if the values of y at time t, t-1 and t-2 are -0.3, 0.4 and -0.1 respectively, and the value of u at time t-1 is 0.3? y_t = -0.1 + 0.75y_t-1 - 0.125y_t-2 + u_t

• A) -0.1
• B) 0.27
• C) -0.34
• D) 0.30

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Definitions:

Main Winding

The primary coil or loop of wire in a motor or generator that creates a magnetic field when energized.

Run Winding

The winding in a motor that is energized during normal operation to produce torque.

Fractional Horsepower

A term describing motors that have a power rating less than one horsepower, often used in low-power applications.

Induction Motors

A type of electric motor that operates on the principle of electromagnetic induction, where the rotor is not directly supplied with electrical power but obtains it via magnetic fields from the stator.