Questions on multiple linear regression, Use SAS or R and include your codes.
A chemical engineer is investigating how the amount of conversion of a product from a raw
material (y) depends on reaction temperature (X1) and reaction time (X2).
He has developed the following regression models:
1. = 100 + 0.2X1 + 4X2
2. = 95 + 0.15X1 + 3X2 + 1X1X2
Both models have been built over the range 20 ≤ X1 ≤ 50 (°C) and 0.5 ≤ X2 ≤ 10(hours).
a. Using both models, what is the predicted value of conversion when X2 = 2 in terms of X1?
Repeat this calculation for X2 = 8. Draw a graph of the predicted values as a function of
temperature for both conversion models. Comment on the effect of the interaction term in
model 2.
b. Find the expected change in the mean conversion for a unit change in temperature X 1 for
model when X2 = 5. Does this quantity depend on the specific value of reaction time selected?
Why?
c. Find the expected change in the mean conversion for a unit change in temperature X 1 for
model 2 when X2 = 5. Repeat this calculation for X 2 = 2 and X2 =8. Does the result depend on the
value selected for X2 ? Why?
