5.X6

Researchers at an agricultural center compared four different preservatives
to be used in freezing strawberries. They prepared the yiel from a strawberry
patch for freezing and randomly divided it into four equal groups. Within 
each group they treated the strawberries with the appropriate preservative 
and packaged them into 8 small plastic bags for freezing at 0 degrees celsius
for a period of 6 months. At the end of this time, the contents of each 
bag were allwoed to thaw and then rated on a scale of 1 to 10 points for 
discoloration (higher scores mean more discoloration). Use the summary 
statistics and partial ANOVA table to answer the following questions.

 group discoloration.Mean discoloration.SD
     1             8.3125           1.0670
     2             6.4375           1.0155
     3             4.0000           0.8452
     4             2.5000           0.9636

>  summary(mod.aov)
                 Df Sum_Sq Mean_Sq F_value   Pr(>F)    
as.factor(group) ** 159.19    ****   *****    *****
Residuals        **  26.69    ****     

a) Test the HOV assumption. Give the statistic, df, critical value and a 
conclusion at the 0.05 level.

b) Fill in the missing value in the ANOVA table and state a conclusion for 
the overall ANOVA F-test.

c) Compute a 95% confidence interval for the mean rating in group 2 based on 
the ANOVA. State an interpretation of the CI.

d) Based on your answer to part (b), conduct a test of the post-hoc 
hypothesis that there is no difference between groups 3 and 4 using 
Fisher's LSD method. Give the statistic, df, and p-value.

e) Conduct a test of the post-hoc hypothesis that there is no difference 
between groups 3 and 4 using Bonferroni's method correcting for all pairwise
comparisons. Give the statistic, df, and p-value.