Estimated the regression for quantity demanded

Question

Problem:

Starting with the data on the price of a related commodity for years 1986 to 2005 listed below, we have estimated the regression for the quantity demanded of a commodity (which we now label Qˆ_X), on the price of the commodity (which we now label P_X), consumer income (which we now label Y), and the price of the related commodity (P_Z), and we obtained the following results.

Year              Pz($)	1986 14	1987 15	1988 15	1989 16	1990 17
Year              Pz($)	1991 18	1992 17	1993 18	1994 19	1995 20
Year              Pz($)	1996 20	1997 19	1998 21	1999 21	2000 22
Year              Pz($)	2001 23	2002 23	2003 24	2004 25	2005 25

Q ^x = 121.86 – 9.50Px + 0.04Y – 2.21Pz
                      (5.12)     (2.18)    (-0.68)
R2 = 0.9633     F = 167.33       D – W = 2.38

Evaluate the above regression results in terms of the signs of the coefficients, the statistical significance of the coefficients and the explanatory power of the regression (R²). The number in parentheses below the estimated slope coefficients refer to the estimated t values.  The rule of thumb for testing the significance of the coefficients is if the absolute t value is greater than 2, the coefficient is significant, which means the coefficient is significantly different from zero.  For example, the absolute t value for Px is 5.12 which is greater than 2, therefore, the coefficient of Px, (-9.50) is significant.  In other words, Px does affect Qx. If the price of the commodity X increases by $1, the quantity demanded (Qx) will decrease by 9.50 units. (c) X and Z are complementary or substitutes?