Instead, this research argues that the simple rank size rule is the general formula and other distributions should be explained as variations of the general principle. The situation is complicated by the fact that the ranked empirical data never exactly equal a slope of 1.000. Almost every rank size researcher has considered, in some fashion, the issue of the slope of unity. He argues that given an initial distribution of different sizes of firms, concentration takes place which results in the elimination of large numbers of smaller firms and the creation of a few larger ones. Similar principles obviously apply to urban areas.
Some firms continue to grow while numerous smaller firms attempt to get started.
In theory, a variety of mechanisms operate to maintain equilibrium. For example, continuous development of larger firms implies a successful industry and thus more small firms enter. If the growth rate of firms declines, mortality of firms is increased and the process is reversed. The significance of the slope of unity is that, in theory, at this value, growth of firms can continue indefinitely. Steindl states that the tendency to concentrate is to some extent endemic, which explains why the Pareto coefficient hovers round a level of 1.1 or so in most cases.