Conjoint analysis is a scaling method originally developed in mathematical psychology. 
Today it is used in many of the social sciences and applied sciences including marketing, 
product management, and operations research. 
It is used for measuring each factor�fs contribution to the whole evaluation of 
products consisting of some factors, for example, 
in testing customer acceptance of new product designs, 
in assessing the appeal of advertisements and in service design.
TRADE-OFF is a method of conjoint analysis used for 
measuring the part worth value of factors in the total evaluation,
exclusively using when evaluations is non-metrical data. 
The part worth values obtained by TRADE-OFF give an approximate comparison of 
each factor's contribution to the total evaluation, 
but it is impossible to utilize their contributions for statistical use since 
they are usually obtained by numerical solution. Moreover, their solution isn't correct 
and unique. And it is known that the part worth value obtained by 
In this paper, we show the problems of TRADE-OFF and then propose a method to obtain 
its definite solution.