Popcorn revisited. A student runs a two-factor experiment to test how microwave power and temperature affect popping. She chooses 3 levels of Power (low, medium, and high) and 3 Times (3 minutes, 4 minutes, and 5 minutes), running one bag at each condition. She counts the number of uncooked kernels as the response variable.
a) What are the null and alternative hypotheses for the main effects?
b) How many degrees of freedom does each factor sum of squares have? How about the error sum of squares?
c) Should she consider fitting an interaction term to the model? Why or why not?