Able 9.23 on page 512 lists the gas requirements for cooking a
roast to 160 degrees under several conditions. The factors are Oven
Setup (levels: "Preheated" or "Not Preheated") and Meat Condition
(levels: "Fresh", "Frozen", "12-hour Thawed", and "24-hour Thawed").
There were 5 observations assigned to each combination of factor levels.
The data are given on the course web page as "roastdata. txt".(a) At a 5% significance level, test whether we can conclude that
there is a significant difference in mean gas usage across cells.
(Give the test statistic value and P-value for this test.)

(b) At a 5% significance level, test whether there is a significant
interaction between Oven Setup and Meat Condition. If so, interpret
what this result is saying. (Give the test statistic value and
P-value for this test.)

(c) Create an interaction plot (specifically, plot gas against meat
condition, for each type of oven setup) and state what this tell you
about the joint effect of Oven Setup and Meat Condition on gas usage.

(d) At a 5% significance level, is there a significant difference in
mean gas usage between preheated and non-preheated ovens, when the meat
is thawed for 24 hours? Use an ESTIMATE statement to answer this
question -- be careful to set it up correctly! (Give the test statistic
value and P-value for this test.)

(e) At a 5% significance level, is there a significant difference in
mean gas usage between fresh meat and all non-fresh meat, when the oven
is preheated? Use an ESTIMATE statement to answer this question -- be
careful to set it up correctly! (Give the test statistic value and
P-value for this test.)

(f) Consider Tukey's procedure for checking for significant differences
between each pair of factor levels. At the 5% level, two combinations
have a significantly different mean gas usage if their sample means differ
by more than what value?