These industries deviate from one or another of the four characteristics of P-competition, but also involve some competition among two or more firms selling close substitutes, if not the same products. Unlike price competition, nonprice competition may be costly and may or may not make consumers better off all in all. Nonprice competition is a mixed bag, but most economists are persuaded that, on the whole, more competition among sellers is better than less. But there is some evidence that the intensity of price competition increases as the number of firms gets larger and their size gets smaller, relative to the industry. These problems mean that the decisions of imperfectly competitive firms are strategic in a sense that monopoly decisions and the decisions of P-competitive firms are not.
Imperfect competition remains a controversial area in economics.
This latter view has become more widespread and influential over the past 30 years, and that change has contributed to the political climate that led to deregulation in the years since 1977.