CBC prohibitions

Prohibitions prevent specific attribute levels from appearing together within the same product concept — for example, preventing a particular brand from appearing at a certain price point. Their primary use is avoiding obviously impossible combinations.

Use prohibitions sparingly. Best practice is to structure your attributes and levels so that any level can freely combine with any other. Prohibitions typically reduce the precision of preference scores, and even rare but not impossible combinations are usually better to include — they contribute to more precise estimation of each attribute level. During analysis, you can avoid these combinations in the market simulator without affecting the underlying data.

If too many prohibitions are specified, Discover will warn you and prevent you from proceeding. Prohibitions may also increase the recommended number of CBC tasks.

1. Navigate to the Design tab of your exercise.
   
2. Click Manage next to Prohibitions.
   
3. Use the dropdowns to select each attribute and level that should not appear together.
   

Preventing one level from appearing with another is called a two-way prohibition. Discover supports up to N-way prohibitions, where N is the total number of attributes in the exercise. For example, prohibiting brand-x, color-2, and price-3 together is a three-way prohibition. Add additional attributes and levels to a prohibition by clicking the plus icon () next to it.