14.31 The article “Effect of Manual Defoliation on Pole Bean Yield” (Journal of Economic Entomology [1984]:

1019–1023) used a quadratic regression model to describe the relationship between y 5 yield (kg/plot)

and x 5 defoliation level (a proportion between 0 and 1). The estimated regression equation based on n 5 24 was y⁄

5 12.39 1 6.67x1 2 15.25x2 where x1 5 x and x2 5 x2. The article also reported that R2 for this model was .902.

Does the quadratic model specify a useful relationship between y and x? Carry out the appropriate test using a .01 level of significance.