24. Refer to Table 9.13 Let y = birth rate and X = women's economic activity

a) Fit the straight-line regression model. Interpret coefficients.

b) Fit the quadratic regression model, and interpret parameters.

c) Using the quadratic fil. find the X-value at which predicted birth rate takes its minimum value is the prediction equation decreasing over the entire range of observed X-values?

d) Does the quadratic model provide a much improved fit over the linear model? Answer (i) descnptively, by comparing R-values. (ii) inferentially, by conducting a test for the quadratic effect. (iii) graphically. by plotting the two fils through the scatter diagram.