The purpose of this paper is to describe the transition of transactional dependency between Japanese carmakers and their tier-1 suppliers from 1993 to 2014. This paper consists of two parts. In the first part, the author proposed the variable named “the degree of transactional dependency of suppliers” (in the paper, Sup's-DEP) and calculated each supplier's dependency from its transaction data. The data was collected from a data book series which contains detailed transaction data of 128 auto parts. From the analysis, construct validity of this variable was almost confirmed by the fact that the degree of dependency negatively affected supplier's profit ratio.
In the next part, the author applied this variable to an industry setting. For the purpose, the author created two variables of industry-wide transactional dependency for suppliers and carmakers (in the paper, weighted Sup's-DEP and weighted Car's-DEP). Comparing the two, the author found an adverse trend that the industry-wide dependency of suppliers was decreasing while the dependency of carmakers increased, which implies that the power balance in transaction was shifting from carmakers to suppliers. Carefully looking into around the year 2008, the time this trend started, the author found three types of trends among carmakers: the group of Mazda, Daihatsu and Fuji-Heavy Industry which increased the dependency, the group of Toyota which remained it, and the group of Nissan, Mitsubishi and Honda, which decreased it. Comparing averaged production ratios among these groups, the group which increased the dependency seemed to succeed because its production ratio was getting lower just after the year 2008. From these findings, this paper shows that the policies for parts procurement are different among carmakers and the gaps have been widening.