In the past decade, the number of U.S. companies with controlled share structures has climbed higher, but a new study found their investors sometimes suffer from it.

The research, conducted by the Investor Responsibility Research Centre Institute, a U.S. research firm focused on corporate responsibility and investing, determined that of all the share structures, companies with multiple classes of shares only outperformed their peers when analyzing returns over one year, and fell short over three-, five- and 10-year terms.