Concentration history and market power in US manufacturing industries

For a 1963–1992 panel of US manufacturing industries, the relationship between seller concentration and both price-cost margins (PCMs) and prices is investigated for industries divided by whether concentration has recently increased or decreased. Regressions of PCM in levels and first differences, and price equations in first differences, establish that the positive effect of concentration on prices and profits is always weaker in industries where concentration has recently increased and always stronger in industries where concentration has recently decreased. These results are attributed to the different endogeneity biases in the two samples. Increasing concentration industries are more likely the ones where leading firms have lowered prices to gain share, while decreasing concentration industries are more likely the ones where smaller firms have lowered concentration by lowering prices. An additional conclusion is that the cost-reducing effects of changes in concentration are greater for increasing concentration industries, meaning that increasing concentration industries have lower price increases compared to decreasing concentration industries.