The Data in Concrete2 represent the compressive strength in thousands of pounds per square inch of 40 samples of concrete taken 2, 7, and 28 days after pouring.
a. At the 0.05 level of significance, is there evidence of a difference in the mean compressive strength after 2, 7, and 28 days?
b. If appropriate, use theTukey procedure to determine the days that differ in mean compressive strength.
c. Determine the relative efficiency of the randomized block design as compared with the completely randomized (one-way ANOVA) design.
d. Construct boxplots of the compressive strength for the different time periods.
e. Based on the results of (a), (b), and (d), is there a pattern in the compressive strength over the three time periods?