The Electronic Journal of Biotechnology (Dec. 15, 2003) published an article on a comparison of two yeast extracts, baker's yeast and brewer's yeast. Brewer's yeast is a surplus by-product obtained from a brewery, hence it is less expensive than primary-grown baker's yeast. Samples of both yeast extracts were prepared at four different temperatures (45,48,51, and 54°C); thus, a 2x4 factorial design with yeast extract at two levels and temperature at four levels was employed. The response variable was the autolysis yield (recorded as a percentage).
a. How many treatments are included in the experiment?
b. An ANOVA found sufficient evidence of factor interaction at a = .05. Interpret this result practically.
c. Give the null and alternative hypotheses for testing the main effects of yeast extract and temperature.
d. Explain why the tests, part c, should not be conducted.
e. Multiple comparisons of the four temperature means were conducted for each of the two yeast extracts. Interpret the results shown below.

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Baker's yeast: Mean yield (%): Temperature (C): 54 5 Mean yield (%): Temperature (C): 54 41.1 475 486 50.3 51 48 473 Brewer's yeast: 39.4 492 4845 496