120 Emotional distress in firefighters. The Journal of Human Stress (Summer 1987) reported on a study of the “psychological response of firefighters to chemical fire.” It is thought that the complete second-order model E(y) = b0 + b1 x1 + b2 x21

+ b3 x2 + b4 x1 x2 + b5 x21 x2 where y = Emotional distress x1 = Experience (years)

x2 = 1 if exposed to chemical fire, 0 if not will be adequate to describe the relationship between emotional distress and years of experience for two groups of firefighters: those exposed to a chemical fire and those not exposed.

a. How would you determine whether the rate of increase of emotional distress with experience is different for the two groups of firefighters?

b. How would you determine whether there are differences in mean emotional distress levels that are attributable to exposure group?