The Klein Corporation's marketing department, using regression analysis, estimates
the firm's demand function, the result being
Q = -104 - 2.1P + 3.2I + 1.5A + 1.6Z
R2 = 0.89
Sample = 200 observations
where Q is the quantity demanded, P is the price, I is disposable income, A is advertising expenditure and Z is the price of a competing product.
Are any of the estimated coefficients not statistically different from zero at the 95% level of confidence? If so which ones?