Citation diversity index

What it is

The citation diversity index is the number of distinct domains an LLM cites across a prompt set, normalised by the prompt count. It describes how concentrated or spread out the sourcing is within a category.

Why it matters

Falling diversity in a category signals consolidation around a few trusted sources and a closing window for new entrants, so it is an early warning about how hard future entry will be.

How it works

Practitioners count unique cited domains per prompt set over time and watch the trend, then act faster to establish source authority while the field is still broad.

When it applies

Monitor it when assessing how contestable a category still is or timing an entry into a new topic area.

Examples

• A category where answers once cited a dozen domains now leaning on three
• A new brand entering a topic while diversity is still high and citations are spread
• A strategist using a sustained drop in diversity to justify investing early

How it is measured

• Distinct cited domains divided by prompt count
• Trend in diversity index over successive runs
• Concentration of citations in the top few domains
• Diversity index compared across related categories