PageRank Leakage

PageRank (or PR) leakage

Whether PageRank Leakage exists or not, is a question of semantics. The PageRank for a given page is solely determined by the inbound links.(1) However, as the spreadsheet will show, an outgoing link can drain the entire site for PageRank.

We have just set up two separate sites - with one page (named Page5) linking to a page in the other site. A picture of the spreadsheet can be found here).

Then we studied how the linked-to site was able to increase its PageRank. We will now look at how the linking site fares.

PageRank leakage - 1. iteration
First iteration
We had guessed at first, that the PageRank transferred from one site to the other would be 0.85 * (1/5) = 0.17. If we look at the first iteration (picture to the right), we see that Page5 has retained all of its PageRank - since PageRank isn't influenced by outbound links. This is what makes many people declare that PageRank leakage doesn't exist.

The Page Ranks of the 4 other page have dropped, however, since they are now getting a smaller share of Page5's PageRank. The loss equals 0.425 per page for a total of 0.17 - exactly as we predicted.

PageRank leakage - 2. iteration
Second iteration
Those 4 pages now have less PageRank to pass back to Page5, so in the next iteration all 5 pages get a lower PageRank. The total PageRank of this mini-site is no longer 5 or 4.83, but 4.6855.

PageRank leakage - 3. iteration
Third iteration
At the third iteration, the total PageRank is 4.568816. As you have guessed by now, it's the same mechanism that we just saw in action when we studied PageRank increase, but when it's shown - graphically - like this, it doesn't feel like a leak - more like a haemorrhage!

PageRank leakage - final. iteration
Many iterations later
Let's skip forward a few hundred iterations and behold. The total PageRank is now a mere 4.054473 - the total loss from our site was much higher than we expected.

And notice another curious thing: For every iteration the leaking page (i.e. Page5) has the highest PageRank in this mini-site. The other 4 pages have even lower PageRank because Page5 isn't doing its part. This slight difference in PageRank will probably not have an effect in the real world - but if anybody tells you their pages perform better when they link out - give it a thought.

A final note: This does not mean that you shouldn't link out.(2) PageRank is only one part of Google's algorithm. I'm personally convinced Google have lots of other ingredients in their secret sauce, which will reward sites that links out.

And now for The Big Picture

(1) This discussion is only about the PageRank formula - in the real Google-world you can also lose PageRank if you link out to "bad neighbourhoods".

(2) On the contrary it's good practise to link to "authority sites" - like this one. :-)