A supermarket chain analyzed data on sales of a particular brand of snack cracker at 104 stores in the chain for a certain 1- week period. The analyst tried to predict sales based on the total sales of all brands in the snack cracker category, the price charged for the particular brand in question, and whether or not there was a promotion for a competing brand at a given store (promotion = 1 if there was such a promotion, 0 if not). (There were no promotions for the brand in question.) A portion of the JMP multiple regression output is shown in the figure.
a. Interpret the coefficient of the promotion variable.
b. Should a promotion by a competing product increase or decrease sales of the brand in question? According to the coefficient, does it?
c. Is the coefficient significantly different from 0 at usual α values?

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Respcnse Sales armacy of Pit Requare Square Rot Hean square E 17.9913 Mean ot BRaeponse Cbservatians for Sun e rice 0.434158 0.417182 Source Model le'sm of squares Mean square 묜Ratio 25.5759 24835.761 2368.01 53204.462 a2าจ.sa 100 323.6 Prob> F 356.7692 104 C Total 103 0.0000 40 30 20 10 Parameter Estisates Tezn Intercept Price Category sales 0.1214871 0.01824 .00 Frmoticn by other? -19.9594 3.7004.39 10 123.95375 0.66628 1.61 01106 44.849952 39.93534 11 0.261 -20 -30 -40 -30 Ettece Test 290 310 330 350 370 390 410