To add an interaction, click the Interactions button. All possible interactions load. After adding the interaction, the DOE Model Controls panel collapses. If you do not want to test all of the interactions, open the DOE Model Controls panel, highlight the interactions that you do not want, and click the Remove Term button.
Number of attributes that can change within a choice set: This is usually the total number of attributes, or variables, you are examining. You can enter fewer than the total number of attributes to constrain the total number that can be changed within a choice set. This might be a reasonable thing to do if you had a large number of attributes and you want to make it easier for the respondents to make a choice. For example, a survey might be interested in 20 or more attributes of a cell phone, but show and change only 5 or fewer attributes in a choice set.