| I. Objective: Replicate Example 9.3 in Studenmnund
text on pp. 315-324 analyzing Serial Correlation, the Durbin-Watson Test,
and corrections for Serial Correlation using the chick6.xls
data file discussed in the text. The chick6.xls
file contains US annual information (from 1974-2002) on the following variables:
Y (per capita chicken consumption in pounds), PC (price of chicken in cents/lb.),
PB (price of beef in cents/lb.) and YD (per capital income in 100s of $).
Assignment:
1. Generate descriptive statistics for the Y, PC, PB and
YD variables using EALimdep (click
here
for help). What do they tell us about the average values of
the variables and how much they vary?
2. Run an ordinary least squares (OLS) regression
of Y on PC, PB and YD, and plot the error terms over the differing time
periods (after you specify the Y, ONE, PC, PB and YD variables in the regression,
click on the OUTPUT tab and click on <Plot residuals><Against
variable>< ONE>). Does the plot suggest serially correlated
errors?
3. Write an equation that describes the regression model,
assuming that the errors are serially correlated. Test whether the
ordinary least squares regression results suffers from serial correlation
using the Durbin-Watson test.
4. If the error terms are serially correlated, what
would be the likely consequences for the estimated OLS regression results?
5. Reestimate the regression, using the Cochrane-Orcutt
correction for serial correlation (after you specify the Y, ONE, PC, PB
and YD variables in the regression, click on the OUTPUT tab and
click on the <OPTIONS> tab, and then click on <Autocorrelation><Correct
for Autocorrelation using><Cochrance Orcutt>. Compare the corrected
results to the OLS results.
6. Reestimate the regression, using the Prais-Winsten correction
for serial correlation (after you specify the Y, ONE, PC, PB and YD variables
in the regression, click on the OUTPUT tab and click on the <OPTIONS>
tab, and then click on <Autocorrelation><Correct for Autocorrelation
using><Prais-Winsten>. Compare the corrected results to the OLS
results and the Corchrane-Orcutt results.
7. EALimdep doesn’t print out an R squared for the corrected
results but you can compute the R squared. Note that the R squared
= 1 - (Unexplained Variation / Total Variation). The Total Variation
can be found by squaring the standard deviation of the dependent variable
(Y) and then multiplying by N-1. The Unexplained Variation can be
found by squaring the standard deviation of residuals and then multiplying
by N-#coefficients. Compute the R squareds for both the OLS, the
Cochrane-Orcutt and the Prais-Winsten results and compare.
II. Objective: |