Market Structure

Market structure refers to # and distribution of seller N-firm concentration index: combined market share of N largest firms in the industry
 * But collusion can occur
 * But there can be cutthroat competition with only a few firms

Herfindahl Index: the sum of the squared market share. Less than 0.2 is fierce comp. Between 0.2 and 0.6 is moderate. Over 0.6 is low comp.

Structural Barriers to Entry
 * Control of Essential Resources
 * Economies of Scale and Scope
 * Marketing Advantages of Incumbency

How to identify competitors?
 * Qualitatively?
 * similar products and characteristics?
 * usage similarity?
 * same selling area?
 * Quantitatively?
 * cross price elasticity of demand
 * SSNIP
 * https://en.wikipedia.org/wiki/Small_but_significant_and_non-transitory_increase_in_price