12.56 The following model was estimated for a sample of 322 supermarkets in large metropolitan areas

(Macdonald and Nelson 1991):

log1y2 = 2.921 + 0.680 log1x2 10.0772 R2 = 0.19 where y = store size x = median income in zip-code area in which store is located The number in parentheses under the coefficient is the estimated coefficient standard error.

a. Interpret the estimated coefficient on log x.

b. Test the null hypothesis that income has no impact on store size against the alternative that higher income tends to be associated with larger store size.