The data alfalfa.csv contains 25 observations of crop yield with corresponding factor
levels for the amount of shade, irrigation level, and inoculum treatment type for the seeds
that were planted.
(a) Fit an ANOVA model using yield as the response and shade and inoculum as fixed
main effects; ignore any interactions.
(b) Plot the residual diagnostics and identify issues with the residual plots if any.
(c) Use the model results to display an ANOVA table and coefficient estimates for the fit
model. Is there a significant difference in any of the mean values for the different
shade or inoculum levels? If so, conduct the appropriate test to determine which
means are different.
(d) There is one observation in the data for each combination of shade and inoculum
levels. Use the value for each combination to make an interaction plot for the two
factors. Does it appear there are any interaction effects? Explain why we should or
should not test for these interactions. What would we need to do to be able to test for