For the data in Figure 15.22: (a) the relationship could be investigated by linear regression; (b) an ‘oral squared’ term could be used to test whether there is any evidence that the relationship is...

For the data in Figure 15.22:

(a) the relationship could be investigated by linear regression;

(b) an ‘oral squared’ term could be used to test whether there is any evidence that the relationship is not a straight line;

(c) if an ‘oral squared’ term were included there would be 2 degrees of freedom for the model;

(d) the coefficients of an ‘oral’ and an ‘oral squared’ term would be uncorrelated;

(e) the estimation of the coefficients would be improved by subtracting the mean from the oral temperature before squaring