An analyst studies quarterly data on th e relationship b etw een retail sales (y , in $ millions), gross national product

(x, in $ billions), and a quarterly dum m y d th a t equals 1 if th e sales are for th e 4th quarter; 0 otherw ise. He estim ates th e m odel y = β 0 + β1x + β 2d + β3x d + ε . Relevant regression results are show n in th e accom panying table.

Coefficients Standard Error t Stat p -value Intercept 186553.3 56421.1 3.31 0.0021 x 55.0 4.6 12.08 0.0000 d 112605.8 117053.0 0.96 0.3424 xd – 4.7 9.3 – 0.50 0.6178

a. Interpret th e intercept dum m y. Is it significant at th e 5%

level?

b. Interpret th e interaction variable. Is it significant at th e 5% level?