Question: In an investigation into the effect of deficiencies of trace elements on a variable Y measured on sheep, the data in the following table were obtained.
Suppose we assume the normal regression model for these data with one categorical predictor.
(a) Produce a side-by-side boxplot for the data.
(b) Plot the standardized residuals against the predictor (if you are using a computer for your calculations, also produce a normal probability plot of the standardized residuals). Does this give you grounds for concern that the model assumptions are incorrect?
(c) Carry out a one-way ANOVA to test for any differences among the conditional means of Y given the predictor
(d) If warranted, construct 0.95-confidence intervals for all the pairwise differences between the means and summarize your findings.