This is a response to a question about relevance and trustrank. Hope you like it!
Relevance and trustrank are different things. To appreciate them you have to step back!
Trust rank is a system that shores up the original back rub aglorithm. Links are STILL a good way to work out how important a site is, PROVIDING, you can work out how important the sites are in the beginning. I have written an article about trust rank here http://www.umbrella-consultancy.co.uk/art1-trustrank.htm
So if the BBC sports site, link to my rugby site, and I link to your football site, then there is a definite sports theme going on there right? BUT, and this is the thing here another football site might link to yours, but they have hardly any trusted links pointing to them, so even though they are more closely relevent, their link will not carry as much weight as mine!
There is a lot more to it than this though, for example………
Back further, google use a base 5 sliding scale logarithmic algorithm. Put simply this allows them to raise of lower ANY element in the algorithm by the power of 5 (as in original value X5 X5 x5 x5 x5) so an original value on an element of say 10, could be boosted anywhere from 10 to 30,000 do you see now just how flexible the algorithm can be? So my link to you might get a boost from my trustrank.
Imagine this scenario. I link to your site, ordinary link on topic but nothing special about my link. Then something happens and the BBC link to the same page on my site that links to you WALLOP up goes the value of that link because Google knows it can trust the BBC, so it can trust me to a lesser extent. Now if the link to my site comes from bbc.co.uk/rugby/wales.etc then that is even more themed and i might also get a theming boost as the source is trusted.
Relevance is odd it can include things like clustering, it can include things like semantics.
A page called Tiger does it again, could be relevant to tigers with stripes, or Golf couldn’t it. So how do YOU work out what it is about? The answer is simple, you can’t! You need more information before you can, so WHAT information do you need? When you start to think like this, you are well on your way to building an understanding of SEO
So is a link from a trusted site that is off topic better than a link from an untrusted site that is on topic? Example would a link from my rugby site about ‘pain killer’ be good? This is a GREAT point to understand how semantics work.
Pain killer. If the link from my rugby site is on a page dealing with rugby injuries, first aid, pain relief etc, and the link goes to your page dealing with pain relief in sports injuries, then they are going to be seen as highly semantically linked as they are dealing with sports injuries as a whole, and both sites are associated sports, so they score well on multiple levels of semantic relevance, then that link will carry great link benefit (this is the phrase I have always used). Now a link from the same page on my site, to your home page, will likely not carry as much weight, because it is ONLY semantically linked via sport words on one level of semantic relevance. (hope I have explained that well enough)
Again step back and look at the elements of a link. Google state that they have over 100 elements (I read recently in a transcript of an interview that Larry Page said it is now over 150) they have lots 😀 of elements to their algorithm, and many people count links as one. links are NOT 1 element, they are a few of the elements that are affected by:~
position of link on anchor page
size of text
Surrounding text and links on anchor page
theme of anchor page and site
content of anchor page
anchor text in link
content of target page
PR value of anchor page
Number and destination of links on anchor page
and now we have Trust rank creeping into the equation that can alter all the above in the blink of an eye.
(I have probably missed some other elements but I am typing this off the cuff and have a busy day so don’t have time to read what I have written 😉 )
SO to answer the question
Is it better to have an irrelevant link from a trusted page or a relevant link from a very relevant but not trusted page ?
I will say what I have ALWAYS said when it comes to link building. For link building to work best, and to future proof your links, you should ALWAYS (and this is amazingly simple but some ignore it) link TO and FROM the most relevant pages on sites!
When the web started, academics posted papers, and on those papers they cited OTHER papers. Within these citations that referred to other research that re-enforced the current paper were often links, and these links would go along the lines of ‘doctor x stated in his recent paper called Search Engine Data retrieval in the area covering that…….. .
The words within the parenthesis would be the anchor text used to describe what the user would encounter if they click the link, and chances are that the link would go DIRECTLY to the page that dealt with this information, RELEVANT INFORMATION, relevant to BOTH anchor AND target pages. Now that was at the birth of the web, and now all these years later, some people STILL have not grasped the absolute basics of linking TO and FROM the most relevant pages 🙂
Are we talking currently or long term ‘what is best’? Currently the web is a mess, and google have some high level technology on the sidelines ready to wipe out a LOT of current success through link mongering. Think about it in simplistic terms, because SEO is BASIC SIMPLE stuff that involves interacting with complex technology, but the basics are STILL the core to success.
why would a link on a page full of links, on a site that has hardly any deep links to it, be sen as important? Sites like DMOZ that are in essence pages full of links, score highly because people link to categories within it all the time. NATURAL linkage results in deep links to and from relevant pages within sites. Sites that have 50,000 links to the home page, but hardly any to the inner pages, yet have 1,000 pages of outbound links are OBVIOUSLY manufactured and not natural. THESE are the sites that will feel it most when the new technology is brought in further into the Google algorithm!