20 CHAPTER 3 REVIEW OF CONJOINT ANALYSIS THEORY ...

After the preference model and measuring scale has been selected, the next step is
to determine the presentation methods. The two-factor at a time, full profile, and
pairwise comparison methods are most frequently used in conjoint analysis. The twofactor
at a time approach requires respondents to compare two attributes at a time and
rank the various combinations of attributes from the most to the least preferred. This
approach is the simplest for respondents, since only two attributes are considered at one
time. It has the advantage of reducing information overload, but its principal
disadvantage is it is limited to ranking data only (Gustafsson, 2000). This approach also
prevents respondents from making realistic choices most commonly used for verbal
descriptions of factor combinations, rather than pictures. (Green and Srinivasan 1978).
Another disadvantage to this approach is its inability to use fractional factorial stimuli to
reduce the number of comparisons (Hair et al., 1998)
An alternative approach, the full-profile method, more closely represents real
buying situations because it utilizes the complete set of attributes. However, this
procedure lends itself to information overload and reduces the accuracy of respondents’
preference evaluation. The number of profiles respondents have to evaluate can be
reduced through the use of fractional factorial designs. For this reason, it is used most
frequently in conjoint analysis. For example, assume you wish to evaluate three
attributes, each with three levels, a total of 27 different product profiles can be evaluated.
This is too large a number of profiles for respondents to effectively rate or rank. Because
of this problem, the full profile procedure is used for relatively small numbers of factors
such as five or six. In many marketing studies, products and services are defined by many
more attributes each a with corresponding large number of levels. The use of a full-
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