Designing the Survey

Conjoint uses the full-profile approach where respondents rank alternative products defined by specific levels of all factors. Even after careful selection of the factors and levels for a study, the total number of potential product combinations is frequently too large for subjects to judge. For instance, with 5 factors and 3 levels for each factor, the number of combinations is 243 (3 × 3 × 3 × 3 × 3).

To solve this problem, the full-profile approach uses what is termed a fractional factorial design, which presents a suitable fraction of all possible combinations of the factor levels. The resulting set, called an orthogonal array, is designed to capture the main effects for each factor level. Interactions between levels of one factor with levels of another factor are assumed to be negligible.

The Generate Orthogonal Design procedure is used to generate an orthogonal array and is typically the starting point of a conjoint analysis.

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