An additive regression model for the Apple prices is:

Dependent variable is: Apples R squared = 51.9% R squared (adjusted) = 34.9%

s = 0.1108 with 47 - 13 = 34 degrees of freedom Variable Coefficient SE(Coeff) t-ratio P-value Intercept -114.825 29.46 -3.90 0.0004 Time 0.057746 0.0147 3.94 0.0004 Jan -0.001438 0.0783 -0.018 0.9855 Feb -0.007062 0.0783 -0.090 0.9287 Mar 0.003626 0.0784 0.046 0.9634 Apr 0.015064 0.0784 0.192 0.8488 May 0.058751 0.0785 0.749 0.4592 Jun 0.115689 0.0786 1.47 0.1501 Jul 0.173627 0.0787 2.21 0.0342 Aug 0.169815 0.0788 2.16 0.0383 Sep 0.049253 0.0789 0.624 0.5368 Oct 0.006191 0.0791 0.078 0.9381 Nov -0.014249 0.0847 -0.168 0.8675

a) What is the name for the kind of variable called Jan in this model?

b) Why is there no predictor variable for December?