Researchers from the Department of Fruit Crops at a university compared four different p...

Researchers from the Department of Fruit Crops at a university compared four different preservatives to be used in freezing strawberries. The researchers prepared the yield 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 eight small plastic bags for freezing at 0°C. The bags in group I served as a control group, while those in groups II, III, and IV were assigned one of three newly developed preservatives. After all 32 bags of strawberries were prepared, they were stored at 0°C for a period of 6 months.At the end of this time, the contents of each bag were allowed to thaw and then rated on a scale of 1 to 10 points for discoloration. (Note that a low score indicates little discoloration.) The ratings are given here:

a. Use the following plots of the residuals and a test of the homogeneity of variances to assess whether the conditions needed to use AOV techniques are satisfied with this data set.

b. Test whether there is a difference in the mean ratings using α = .05.

c. Place 95% confidence intervals on the mean ratings for each of the groups.

d. Confirm your results with the computer output given here.