Have an idea?

Visit Sawtooth Software Feedback to share your ideas on how we can improve our products.

CBC design: selecting levels

When designing my CBC experiment, I carefully select the levels for each attribute respecting these considerations that are often mentioned across studies:
- the number of levels should be similar across attributes (minimum of 3, ideally 5).
- the range of your levels per attribute should include the different values that you want to observe in your study for that attribute
- the range of your levels should not go beyond the realistic values of the attribute

However I don't find any recommendation on the selection of the values within that range. Let us say I have the price attribute and my product can range between 10€ and 50€. If I want to limit the number of levels per attribute to three, can I use 10€, 20€ and 50€? Or should I use a more linear evolution of the price like 10€, 30€ and 50€? Would the first evolution create a bias? Do you know documentation/paper that deal on that topic?

Thank you
asked Apr 12, 2016 by Philippe Lebeau

1 Answer

0 votes
These are good questions.  You usually hope to pick psychologically important price increments for respondents that capture the "elbows" (points of non-linearity) that you think might exist across the price range.

Using only 3 price points only gives you one opportunity to set an elbow into the function.  I prefer to use 4 or 5 price points whenever I can afford it.

Usually, researchers pick either equidistant increments, or increments that start smaller and then get bigger toward the right part of the price range.

Some advanced conjoint researchers employ truly continuous price variations such that across respondents potentially dozens or hundreds of unique price points have actually been shown to respondents.  Then, they fit "piece-wise" (like a spline) functions to the data to investigate and model the points of non-linearity along the function.  This is the "Summed Price" approach as can be done automatically within the ACBC (adaptive CBC) system.
answered Apr 12, 2016 by Bryan Orme Platinum Sawtooth Software, Inc. (152,955 points)
How to code/implement splines in CBCHB?