PageRank Leak

PageRank is an often misunderstood concept.

Essentially, PageRank (PR) can be considered as a scoring mechanism that allows a web page to pass a portion of its score through a link to another web page. This portion is dependent on two things - a "weighting" which prevents PR from spiralling out of control, and the number of links on the web page on which the link appears.

If all the links on the page are internal (i.e. pointing to other URLs on the same website) then all the PR is passed to other pages on the same site (minus the weighting). However, if one of more of the links point to pages on other websites, that portion of PR is passed out from the current website.

Many webmasters consider such loss to be leakage, not because the page on which the link appears loses any PR (in fact the mechanism does not reduce the PR of this page), but because internal links are considered to "recycle" PR around the current site, whereas outbound links send PR to other sites.

However, as Google is in the habit of penalising closed networks (which includes websites or collections of sites that do not link out), such leakage can be considered part of the price of continuing to be included in Google's index.

Additionally, outbound links have many other benefits, both to users and to search engine optimisation.