DoE for conjoint analysis

Why do we use design of experiments for conjoint analysis

The principle of conjoint analysis is to present a set of products (also known as profiles) to the individuals who will rank, rate, or choose some of them.

In an ideal analysis, individuals should test all possible products. But it is soon impossible; the capacity of each being limited and the number of combinations increases very rapidly with the number of attributes (if one wants to study five attributes with three categories each, that means already 243 possible products). We, therefore, use the methods of experimental design to obtain an acceptable number of profiles to be judged while maintaining good statistical properties.

XLSTAT-Conjoint analysis software includes two different methods of conjoint analysis:

1. the full profile analysis
2. and the choice based conjoint (CBC) analysis.

Design of experiments for full profiles conjoint analysis

The first step in a conjoint analysis requires the selection of a number of factors describing a product. These factors should be qualitative. For example, if one seeks to introduce a new product in a market, we can choose as differentiating factors: the price, the quality, the durability ... and for each factor, we must define a number of categories (different prices, different lifetimes ...). This first step is crucial and should be done together with experts of the studied market.

Once this first step is done, the goal of a conjoint analysis is to understand the mechanism of choice: Why people choose one product over another?

To try to answer this question, we will propose a number of products (combining different modalities of the studied factors). We can not offer all possible products, so we will select products by using a design of experiments before presenting them to people who will rate them or rank them.

The full profile method is the oldest methods of conjoint analysis; we seek to build an experimental design that includes a limited number of full profiles that each individual interviewed will then rank or rate.

XLSTAT-Conjoint analysis software uses fractional factorial designs in order to generate profiles that will then be presented to respondents. When no design is available, XLSTAT-Conjoint uses algorithms to search for D-optimal designs.

Prohibited combinations option 

For some experimental designs, categories combinations are not feasible. This may be due to different reasons: equipment, products, ... In these cases, it is possible to indicate these prohibited combinations, the generated experimental design will not take them into account.