In some media industries, the same number of companies control ownership today as in the 1950s. There are five major movie studios today, for example, compared to the same number of major studios in the 1940s. The number of broadcast stations and the number of magazines has increased since the 1940s, but the number of newspapers, magazines and recording companies has declined. Overall, however, American media ownership has been contracting rather than expanding. This is because large companies are buying small companies. The trend is for media companies to cluster together into big groups, which means that a small number of companies now control many aspects of the media business. This trend, called concentration of ownership, takes four different forms: chains, broadcast networks, conglomerates and vertical integration.