An experiment analyzed how the mean corn yield varied according to three factors: nitrogen-based fertilizer, phosphate-based fertilizer, and potash (potassium chloride)-based fertilizer, each applied at low and at high levels.
a. How many groups result from the different combinations of the three factors?
b. Defining indicator variables, state the regression model that corresponds to an ANOVA assuming a lack of interaction.
c. Give possible estimates of the model parameters in part b for which the estimated corn yield would be highest at the high level of nitrogen fertilizer and phosphate fertilizer and the low level of potash.