A pharmaceutical firm wanted to obtain information on the relationship between the dose level of a drug product and its potency. To do this, each of 15 test tubes was inoculated with a virus culture and incubated for 5 days at 30° C. Three test tubes were randomly assigned to each of the five different dose levels to be investigated (2, 4, 8, 16, and 32 mg). Each tube was injected with only one dose level, and the response of interest (a measure of the protective strength of the product against the virus culture) was obtained. The data are given here.

Dose Level                  Response

2………………………… 5, 7, 3

4…………………….. 10, 12, 14

8…………………….. 15, 17, 18

16…………………… 20, 21, 19

32……………………. 23, 24, 29

a. Plot the data.

b. Fit both a linear and a quadratic model to these data.

c. Which model seems more appropriate?