The relative importance of individual product attributes can be measured more accurately when respondents evaluate them as a single stimulus (CONsidered JOINTly) than when each attribute is evaluated in isolation:

• Many consumers are unable to determine the relative importance of individual product attributes.
• Individual attributes are perceived differently in isolation than in the combination that makes up a whole product.
• Constructing the preferred combination of attributes strains respondents' cognitive abilities — “all attributes are important.”
• Social desirability and a sharply defined self-image motivate respondents to give some attributes great weight even when they play no role (e.g. environmental friendliness, wealth, reduced importance of price).
• Some respondents deliberately try to manipulate the results by giving “advantageous” answers (e.g. overstating the importance of price).