Recently, SEO firm Fortune Interactive published the first part of a study that measured "Varying Degrees of Importance for On-page and Off-page Factors" on search engine rank.

[fortuneinteractive.com...]

They conclude that the QUALITY of the originating page from where the inbound link comes is by far the most important SE rank factor. To quote:

IBL Quality "...is a measurement of key elements on the page containing an in-bound link which, in combination, influence the link reputation for the target of the link. This is the only factor that had the same level of relative influence across the search engines and happened to be the most influential in all cases."

There are some interesting results and conclusions. I recommend that you read the report.

They don't go into any detail on the criteria for measuing quality. They mention "key elements" and "reputation". What do you think is behind this quality measurement?