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) |
|
|
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 }