GoogleGuyがPageRankとバックリンクに関して次のような発言をしています。
One thing that I noticed in the first 300 posts or so was a discussion about whether backlinks or PageRanks were also being updated at the same time. In general, I wouldn't fixate too much on backlinks or PageRank during an update. The external backlinks/PR that we show have at least a couple factors that complicate analysis. First off, they are a snapshot in time, and the actual backlinks/PageRank used for ranking are from a different time interval. Another complicating factor is that we don't show every backlink on Google; we only show a subset of the backlinks we have internally. [One of the things we needed to do on our webmaster pages revamp was to go back and make sure it's clear that we only show a sampling of the backlinks we know about, not all backlinks.] The snapshotting + asynchronous nature + subsampling actions means that it's pretty hard to trace the reason for a ranking change back to a particular exported view of backlinks or PageRank. This is an area where I wouldn't read as much into the particular backlinks or PageRank that you see at any particular instant in time. Also, if a backlink or PageRank external update happened at the same time as ranking changes, I wouldn't read too much into how closely in time they happen together.Just as a guide for people who don't eat and breathe WebmasterWorld, we typically show new backlink sample sets every 3-5 weeks or so. We have a bank of machines that computes PageRank continuously (and continually, I suppose; I wasn't an English major), but we only export new visible PageRanks every 3-4 months or so.
[GoogleGuy's posts Some posts and advice on Bourbon and other topics, WebmasterWorld]
要旨『私たちが普段目にしているGoogleのPageRankやバックリンク情報は、過去のある時点の情報であり、実際の（今まさに目にするGoogleの出力する検索順位を決定付けている）PageRankやバックリンクとは異なる。また、link: で検索した時にGoogleが表示するバックリンクはサブセットのサンプリングに過ぎず、全てを表示しているわけではない。以上、「情報は過去のものであり同期していないこと」「バックリンクのサンプルに過ぎないこと」を踏まえると、Googleにおける検索順位に変化があった際に、その変化理由を求めることは非常に困難ということである』
