Final answer:
In this question, we determine which option should not include an interaction among given options.
Step-by-step explanation:
In this question, we are given options a. - d. and we need to determine which option should not include an interaction. Let's analyze the options:
a. Between levels of a qualitative variable: In this case, we would include an interaction to explore how different levels of the qualitative variable interact with each other.
b. Between quantitative and qualitative variables: Including an interaction here would help us understand how the quantitative and qualitative variables influence each other.
c. Between quantitative variables: Including an interaction in this case would allow us to examine the relationship between the two quantitative variables.
d. Between qualitative variables and squared quantitative variables: Including an interaction here would help us understand how the qualitative and squared quantitative variables interact.
Based on the above analysis, the correct answer is d. Between qualitative variables and squared quantitative variables, as including an interaction for these two types of variables is not necessary.