Final answer:
Ratios compared over time for a firm's evaluation are referred to as trend analysis or time series analysis. The Four-Firm Concentration Ratio and Herfindahl-Hirschman Index are used to assess market competition levels.
Step-by-step explanation:
When ratios are used to evaluate a firm and they are compared across time it may be referred to as trend analysis or time series analysis. The Four-Firm Concentration Ratio and the Herfindahl-Hirschman Index (HHI) are tools used to measure the degree of monopoly power in an industry. The Four-Firm Concentration Ratio measures the combined market share of the largest firms in an industry, typically the top four to eight, indicating how much of the market is controlled by the largest companies. The HHI takes it a step further by squaring the market shares of all firms in the market and summing the total, providing a more nuanced view of market competition.