Market Concentration
We use the Herfindahl–Hirschman Index (HHI) to measure how concentrated or competitive each market segment is over time. The HHI ranges from 0 to 1, with the following general guidelines:
- <0.10: Very competitive market
- 0.10 - 0.15: Competitive market
- 0.15 - 0.25: Moderate concentration
- 0.25 - 0.5: Concentrated market
- >0.5: Very concentrated market
See the HHI Explained page for an interactive tool that illustrates how HHI relates to market share distributions.
Concentration is measured across three groups: Powertrain, Vehicle Type (Body Style), and Price Bin. Within each group, you can choose a level and HHI dimension to view: make, vehicle type (body style), and price bin. The map below allows you to select any of these dimensions for any listing year for every U.S. census tract.
Below the map are boxplots that summarize the distribution of HHI values across all census tracts for a given year. Use the timeline slider below each chart to switch between years.