Final answer:
The Herfindahl-Hirschman Index (HHI) is an economic measure of industry concentration. To calculate it, one must square the market shares of all players or entities within the market and sum these numbers. Specific data on market shares is required to evaluate the competitiveness of each Tennis Grand Slam.
Step-by-step explanation:
The Herfindahl-Hirschman Index (HHI) is a measure of market concentration and competition among firms within an industry. To calculate the HHI, you should square the market share of each firm, which represents their relative size, and sum these values. For the Tennis Grand Slams (Australian Open, Roland Garros, Wimbledon, US Open), you would need to do this for all players or entities associated within each tournament's market between the years 2009 and 2019. However, there is not enough information provided to complete the calculation, as we would need the individual market shares of each player or entity for that period.
Without the specific market shares, we cannot calculate the HHI and determine which Grand Slam is the most or least competitive. In general, the closer the HHI is to 0, the more competitive the industry; the closer to 10,000 (reflecting a 100% market share squared), the less competitive it is as it indicates a monopoly.