Many people assume that personality must be related to consumer behavior. Knowing a customer's personality profile should help predict what she or he will buy, and how decisions will be made in the marketplace

Researchers, however, have been frustrated in their search for a unified theory of personality that would explain consumer behavior. Use trait theory to explain why this is so.

There is no single theory of personality upon which everyone agrees. The trait theory approach has been used in many studies. These measures, however, are subject to a number of potential problems.
• Many of the scales are not sufficiently valid or reliable; they do not adequately measure what they are supposed to measure, and their results may not be stable over time.
• Psychologists typically develop personality tests for specific populations. The tests may have been developed for a different population than the one being studied in consumer behavior.
• The tests may be used under conditions different from those in which they were designed.
• They may have been modified to fit research conditions that may invalidate the measures.
• Many trait scales measure gross, overall tendencies; marketers use these results to make predictions about purchases of specific brands.
• The scales may not be relevant to measures related to consumer behavior.
In summary, the common sense notion that personality is related to consumer behavior may simply be false. On the other hand, there may be a strong relationship, but it has not been found because of the problems of measuring personality in marketing and consumer settings.