We know that in past Google has shown an interest in maintaining some level of domain diversity. I am not the only one to have complained about Wikipedia dominating the search results at one point or another, and certainly webmasters have felt the squeeze before when domain clustering seemed to fill the search results with just one or two sites at a time. But what is perhaps most remarkable is how steady domain diversity has been in Google over the last 2 years.
- Unique Domains per Keyword (ie: the total number of unique domains divided by the total number of keywords)
- Percentage of Ranking Slots Maintained by the top 2.5% of Domains
- Estimated Traffic Share of Top 2.5% of Domains
- Estimated Value Share of Top 2.5% of Domains
The results were startlingly steady. It is almost uncanny. The number of unique domains per keyword hovered between 5.46 and 4.93 over the last 2 years, roughly 1/2 of 1 domain. The top 2.5% has regularly maintained market share in terms of ranking slots, estimated traffic and estimated traffic value.
Looking at these numbers makes me believe that Google is actively policing domain diversity as a quality metric. While it is pure conjecture, I think this data suggests that Google looks at the impact of future algorithm updates in terms of their impact on an ideal domain-diversity level. This may likely keep the ecosystem fresh and churning, rather than monopolized by a series of mega sites (even though it certainly may not feel that way).