Use factorial plots in conjunction with binary logistic regression. Factorial plots include the Main Effects Plot and Interaction Plot.

A main effect is the change in the mean response from the low level to the high level of a variable. Use this plot for these purposes:

·    examine the level means for each variable

·    compare the level means for several variables

·    compare the relative strengths of the effects across variables

An interaction occurs when the effect of one variable depends on the value of another variable. Each plot displays the interaction between two variables. Use interactions plots to compare the relative strength of the effects across variables.

A cereal company is investigating the effectiveness of a TV advertisement for a new product called Cocoa Crunch. After showing the advertisement in a particular community for one week, they randomly sampled seventy-one adults exiting a local supermarket.

They were asked:

·    whether or not they bought Cocoa Crunch (Bought)

·    their household income (in thousands of dollars) (Income)

·    whether or not they had children (Children)

·    whether or not they viewed the advertisement (ViewAd)

Data: CerealAd.MTW (available in the Sample Data folder).