Sueyoshi et al. (2009) have examined a synergy effect between electricity and gas services in the US electric utility industry. They have compared electricity-specialized firms with diversified utility firms in their financial performance and corporate value. A problem of their study is that it has not empirically measured the operational performance of the electric utility firms. As an extension of the preceding study, this research investigates the operational performance of 104 US electric utility firms (1990-2004) by fully utilizing DEA (Data Envelopment Analysis). This study finds the three new policy implications. First, the synergy effect has not existed in the operational performance of diversified utility firms before and [...]
