In the preliminary studies of a new drug, a pharmaceutical firm needs to obtain information on the relationship between the dose level and potency of the drug. In order to obtain this ­information, a total of 18 test tubes are inoculated with a virus culture and incubated for an ­appropriate period of time. Three test tubes are randomly assigned to each of six different dose levels. The 18 test tubes are then injected with the randomly assigned dose level of the drug. The measured response is the protective strength of the drug against the virus culture. Due to a problem with a few of a problem with a few of the a problem with a few of the test tubes, only two responses were obtained for dose levels 4,

a. Plot the data.
b. Fit a linear regression model to these data.
c. From a plot of the residuals, does there appear to be a possible lack of fit of the linear model?

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Dose level Response 73 101 15,17 20,21,19 23,29 28,31,30 16 32 64