Walmart revenue. Walmart grew rapidly in the years leading up to the financial crisis. Here is the monthly revenue ($Billion) for Walmart from November 2003 to January 2007.

a) What components of a time series do you see in this timeplot?
Here’s a regression model fit using dummy variables for months and a Time variable that counts from 1 for the first data value in the series.
Dependent variable is: WM Rev R squared = 94.3% R squared (adjusted) = 91.6%
s = 1.121 with 39 - 13 = 26 degrees of freedom Variable Coeff SE(Coeff) t-ratio P-value Intercept 12.0322 0.6562 18.3 60.0001 Time 0.145241 0.0163 8.93 60.0001 Feb 1.46096 0.8599 1.70 0.1013 Mar 2.84671 0.8585 3.32 0.0027 Apr 1.67981 0.8574 1.96 0.0609 May 0.870232 0.8567 1.02 0.3191 Jun 4.99999 0.8562 5.84 60.0001 Jul 0.106417 0.8560 0.124 0.9020 Aug 0.434176 0.8562 0.507 0.6164 Sep 3.25327 0.8567 3.80 0.0008 Oct -0.219640 0.8574 -0.256 0.7998 Nov 1.87023 0.7932 2.36 0.0262 Dec 11.5625 0.7927 14.6 60.0001

b) Interpret the coefficient of Time.

c) Interpret the coefficient of Dec.

d) What revenue would you predict for Walmart in February 2007 (the 40th month in this series)?

e) What does it mean that the coefficient for Oct is the only negative coefficient in the model?