Does design module allow for prohibited pairs?

Yes, allows you to prevent specific combinations of levels from showing on the same alternative (under “Advanced settings”). For example, a particular price (say, $5) might be incompatible with a particular size (“recycled”). For best results, we recommend using this option sparingly: not more than four restrictions.

Keep in mind that you only need to prohibit combinations that are unrealistic in the eyes of the consumer, rather than those that are not feasible for the company to make. For example, if consumers would not be surprised to see $5 recycled tissue paper, but it is not feasible for the company, you should not prohibit this pair in the design of your experiment. Instead, you should simply ignore product concepts with this combination when you look at the results of the analysis.

If you find that you need to have more than seven prohibitions, we strongly encourage you to think through these options:

  1. If you are using a generic experiment, you might need a brand-specific conjoint study where you can set which levels apply to which brands.

  2. Remove prohibitions of any pairs that are at least marginally plausible in the eyes of the consumer.

  3. Remove prohibitions of pairs that are plausible to the consumer but not feasible for the company to supply (as discussed above, they should not be prohibited in the design).

  4. Make sure to set other advanced settings to “Automatic”.

Why is there a limit on the number of prohibited pairs I can include in my study?

We limit the number of prohibited pairs you can include in your study based on the number of levels and attributes you have. Without limitation, it would be extremely difficult (and sometimes impossible) to run the analysis on your study.

When there are quite a number of prohibited pairs, we generally recommend:

  • To let the options show without prohibitions (even though some options may not make sense) as this will allow the system to estimate preferences more accurately. When viewing the report, you can simply ignore the concepts that do not make sense.

  • Alternatively, you can use Brand-Specific Conjoint, which allows you to specify the levels that apply to each SKU/brand.

For more tips on attributes and levels, read our guide: Specifying attributes and levels in conjoint analysis.