to ascertain the characteristics of industries in Japan in which cartels were formed. Furthermore, through a comparison with the results of the abovementioned OFT (2005), it is be possible to evaluate the differences between characteristics of European and Japanese industries.

The structure of this paper is as follows. In Section 2, we review empirical research related to the factors promoting the formation and continuation of cartels and factors involved in the prevention of cartels, as well as the length of existence of cartels and factors determining these time periods. Section 3 provides an explanation of the data used in this research. Section 4 explains the results of the empirical analysis and Section 5 concludes this paper.

### 2. Empirical studies concerning the formation and continuation of cartels

There have been a number of researches which investigates factors influencing the formation of cartels. A survey paper by Levenstein and Suslow (2006) covering this kind of researches serves as a reference, and Levenstein and Suslow (2014) intensively surveys empirics in the economic analysis of cartel. As mentioned in the previous section, performing an empirical analysis of structural factors influencing the formation of cartels requires data on all cartels, that is, hidden and uncovered cartels. However because cartel is not usually overt, we cannot do such study except when cartels are operated under legal approval by the government. Below are studies which used almost all the cartels including legal ones approved by the government: Symeonidis (2003) studies relationships between the number of cartels and the structures of industries, Suslow (2005) studies relationships between the length of cartel and the structures of industries, and Jacquemin et al. (1981) studies export cartels in Japan. Those researches are thought to cover all possible cartels that existed during the period of their analysis. Although the present paper only uses cartels data which actions by competition authority were taken, this research will uncover relationships between cartels and the structures of industries in Japan, and by doing so it contributes to test theoretical hypotheses proposed in several theoretical papers.

Symeonidis (2003) applied data on the 1950's UK manufacturing industries (151 industries from the 4-digit category for UK industries) to conduct an empirical analysis of relationships between cartels and the characteristics of industry structures which are the degree of concentration, the growth rate of demand, capital intensity, research and development (R&D), and so on. The study uses samples of the 71 legal cartels formed under the 1956 UK Restrictive Trade Practices Law and 80 competitive industries. According to its result, while there was a high probability of cartels in industries with high capital intensity, cartels in advertising-intensive industries are unlikely to occur compared to less advertising-intensive industries. Regarding relationship with demand growth, the probability of cartels in industries with growing demand was higher than that of industries with stagnant or declining demand growth. Regarding relationship with market concentration, if it controls the endogeneity $ ^{3} $ of the degree of concentration, the