An experiment was conducted to investigate the amount of a particular drug present in the liver of a rat. Nineteen rats were randomly selected, weighed and given an oral dose of the drug. Because it was felt that large livers would absorb more of a given dose than smaller livers, the actual dose an animal received was approximately determined as 40mg of the drug per kilogram of body weight. (Liver weight is known to be strongly related to body weight.) After a fixed length of time each rat was sacrificed, the liver weighed, and the percent of the dose in the liver determined.
The experimental hypothesis was that, for the method of determining the dose, there is no relationship between the percentage of the dose in the liver (Y) and the body weight (X1), liver weight (X2), and the relative dose(X3).
The data are given in Table 1 (click here)
In STATA
a) Conduct all pairwise plots and comment. Do you think there are
any trends in the data?
b) Regress Y on X1, X2, X3. Compute 95% confidence intervals for each coefficient.
c) Plot the fitted values against the residuals. Comment on the pattern.
d) Is the model significant? Which variables seem important. Should a reduced model be used? If so, what is the final model?.