14.10 The relationship between yield of maize, date of planting, and planting density was investigated in the article “Development of a Model for Use in Maize Replant Decisions” (Agronomy Journal [1980]: 459–464).

Let

Transcribed Image Text:

y=percent maize yield xplanting date (days after April 20) x2 planting density (10,000 plants/ha) X2 2 The regression model with both quadratic terms (y = a + B1x1 + B2x2 + B3x3 + B4x4 +e where x3 = x and x4 = x) provides a good description of the rela- tionship between y and the independent variables. a. If a and 4 21.09, B = .653, B = .0022, B3 = 2.0206, 0.4, what is the population regression function? b. Use the regression function in Part (a) to determine the mean yield for a plot planted on May 6 with a density of 41,180 plants/ha. c. Would the mean yield be higher for a planting date of May 6 or May 22 (for the same density)? d. Is it legitimate to interpret B = .653 as the average change in yield when planting date increases by one day and the values of the other three predictors are held fixed? Why or why not?