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March 19, 2007

How Google Blog Search Ranks Results

Unlike most blog search engines, Google Blog Search ranks the results by relevancy. You can change that by clicking on "sort by date", but the default option is useful if you want to find the most significant blog posts about a topic. But how does Google rank blog posts?

A new patent gives us some answers. Google uses indicators to reflect the quality of a blog or of a blog post.

Positive signals
Negative signals (spam signals)
  • links from blogrolls (especially from high-quality blogrolls or blogrolls of "trusted bloggers")
  • links from other sources (mail, chats)
  • using tags to categorize a post
  • PageRank
  • the number of feed subscriptions (from feed readers)
  • clicks in search results
  • posts added at a predictable time
  • different content between the site and the feed
  • the amount of duplicate content
  • using words/n-grams that appear frequently in spam blogs
  • posts that have identical size
  • linking to a single web page
  • a large number of ads
  • the location of ads ("the presence of ads in the recent posts part of a blog")

To rank the search results, Google combines a quality score obtained by mixing those signals with a relevance score (IR score) that depends on the query. "The IR score may be determined based on the number of occurrences of the search terms in the document. The IR score may be determined based on where the search terms occur within the document (e.g., title, content, etc.) or characteristics of the search terms (e.g., font, size, color, etc.). A search term may be weighted differently from another search term when multiple search terms are present. The proximity of the search terms when multiple search terms are present may influence the IR score." (the quote was slightly altered for clarity)

We learned that Google uses all kinds of factors to determine the popularity and the quality of a blog, but that doesn't mean less popular blogs are left out if they have relevant content. You should also try to avoid all the negative signals that may indicate your blog is spammy.

{ via Search Engine Roundtable }

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