 This is actually a topic that I used to put poor innocent new recruits through, particularly if they came from a non-marketing background. Even though this is considered by a lot of people to be an advanced topic, I think it's something that actually it makes sense for people who want to learn about SEO to learn first because it's foundational and if you if you think about a lot of other technical SEO and link building topics from this perspective, they make a lot more sense and are simpler and you kind of figure out the answers yourself rather than needing to read 10,000 word blog posts and patents and this kind of thing. Anyway hold that thought. Because it's 1998, I am six years old and this is a glorious state-of-the-art video game and internet browsing that I do in my computer club at school looks a bit like this. I actually didn't use Yahoo, I used Excite which in hindsight was a mistake but in my defense I was six. The one thing you'll notice about this as a starting point for a journey on the internet compared to something like Google or whatever you use today maybe even like something that's built into your browser these days and there's a lot of links on this page and mostly there are links to pages with links on this page. It's kind of like a taxonomy directory system and this is important because if a lot of people browse the web using links and links are primarily a navigational thing then we can get some insights out of looking at links. There are sort of proxy for popularity. If we assume we assume that everyone starts their journey on the internet on Yahoo in 1998 then the pages that are linked to from Yahoo are going to get a lot of traffic, right? They are by definition popular and the pages that those pages link to will also still get quite a lot and so on and so forth and through this we could build up some kind of picture of what websites are popular and popularity is important because if you show popular websites to users in search results then they will be more trustworthy and credible and likely to be good and this kind of thing. This is massive over simplification there with me but this is kind of why Google won. Google recognized this fact and they came up with an innovation called PageRank which made their search engine better than other people's search engines and which every other search engine subsequently went on to imitate. However, is there anything I said just now relevant 23 years later? We definitely do not primarily navigate the web with links anymore. We use these things called search engines which Google might know something about but also we use news feeds which are kind of dynamic and uncrawlable and all sorts of other non-static HTML link-based patterns. Links are probably not the majority even of how we navigate our way around the web except maybe within websites. And Google has better data on popularity anyway, right? Like Google runs a mobile operating system, they run ISPs, they run a browser, they run YouTube. There's lots of ways for Google to figure out what isn't as popular without building some arcane link graph. However, be that true or not, this still is a core methodology to underpins how Google works on a foundational level. In 1998 it was the case that PageRank was all of how Google worked really, it was just PageRank plus relevance. These days there's a lot of nuance and layers on top and even PageRank itself probably isn't even called that and probably has changed and been refined and tweaked around the edges. And it might be that PageRank is not used as a proxy for popularity anymore but maybe as a proxy for trust or something like that and it has a slightly different role in the algorithm. But the point is we still know purely through empirical evidence that changing how many and what pages linked to a page has a big impact on organic performance. So we still know that something like this is happening and the way that Google talks about how links work in their algorithm still reflects a broadly PageRank-based understanding as do developments in SEO directives and hreflang and relamp and this kind of thing. It still all speaks to a PageRank-based ecosystem if not a PageRank only ecosystem. Also I'm calling it PageRank because that's what Google calls it but some other things you should be aware of that SEOs use. Link equity I think is a good one to use because it kind of explains what you're talking about in a useful way. Link flow it's not bad but link flow is alluding to a different metaphor that you've probably seen before where you think of links as being sent through big pipes of liquid that then pour in different amounts into different pages. It's a different metaphor to the popularity one and as a result it has some different implications if it's overstretched. So use some caution and then linking strength. I don't really know what metaphor this is trying to do and it doesn't seem as bad as linking juice at least fine I guess. More importantly how does it work and I don't know if anyone here hates maths if you do I'm sorry but there's going to be maths. So the initial sort of question is or the foundation of all this is imagine that so A in the red box here that's a web page to be clear in this diagram. Imagine that the whole internet is represented in this diagram that there's only one web page which means this is 1970 something I guess. What is the probability that a random browser is on this page? We can probably say it's one or something like that. If you want to have some other take on that it kind of doesn't matter because it's all just going to be based on whatever number that is. From that though we can sort of try to infer some other things so whatever probability you thought that was and let's say we thought that if there's one page on the internet everyone's on it. What's probability that a random browser is on the one page A links to? So say that we've pictured the whole internet here. A is a page that links to another page which links nowhere and we started by saying that everyone was on this page. Well what's probability now after after a cycle that everyone will be on this page? Well we go with the assumption that there's an 85% chance and the 85% number comes from Google's original 1998 white paper. It's an 85% chance that they go on to this one page in their cycle and 15% chance that they do one of these non-browser based activities. The reason why we assume that there's a chance on every cycle that people exit to do non-browser based activities is because otherwise we get some kind of infinite cycle later on. We don't need to worry about that but the point is that if you assume that people never leave their computers and that they just browse through links endlessly then you end up assuming eventually that every page has infinite traffic which is not the case. That's the starting point where we have a really simple internet. We have a page with a link on it and a page without a link on it and that's it. Something to bear in mind with these systems is obviously web pages don't have a link on them and web pages with no links on them are virtually unheard of like the one on the right. This gets really complex really fast if we try to make a diagram just of two pages on the Moz website it would not fit on this screen right. So we're talking in really simplified versions here but it doesn't matter because the principles are extensible. So what if page on the left actually linked to two pages not one? What is the probability now that we're on one of those two pages? We're taking that 85% chance that they move on at all without exiting because the house got fired they went for a bike ride or whatever and we're now dividing that by two. So we're saying 42.5% chance that they were on this page 42.5% chance you're on this page and then that you know nothing else happens because there's no more links in the world that's fine. What about this page? So if this page now links to one more how does this page of strength relate to page eight? So this one was 0.85 over two and this one is 0.85 times that number so we die note that we're diluting as we go along because we've applied that 15% deterioration on every step. This is useful and interesting to us because we can imagine a model in which page A on the left is a home page and the page on the right is some page we want to rank and we're diluting with every step that we have to jump to get there and this is crawl depth which is a metric that is exposed by MozPro and most other technical SEO tools that that's why crawl depth is something that people are interested in is this and part of it is discovery which you won't get into today but part of it is also this dilution factor and then if this page actually linked to three then again each of these pages is only one third as strong as when it only linked to one so there's the it's being split up and diluted further down we go so that all got very complicated very quick on a very simple fictional website don't panic the lessons we want to take away from this are quite simple even though the the mass becomes very arcane very quickly so the first lesson we want to take is that each additional link depth diluted value so we talked about the reasons for that but obviously it has implications for site structure it also has implications some other things some other common technical SEO issues that I'll cover in a bit so if I link to a page indirectly that is less effective than linking to a page directly even in a world where every page only has one link on it which is obviously an ideal scenario the other takeaway we can we can have is that more links means each link is less valuable so if every additional link you add to your home page you're reducing the effectiveness of the ones that the links are already there and so this is this is very important because if you look on a lot of sites right now you'll find 600 link mega nabs at the top of the page in the same at the bottom of the page and all this kind of thing and that can be a that can be an okay choice the I'm not saying that's always wrong but it is a choice and it has dramatic implications some some of the biggest changes in SEO performance I've ever seen on websites came from cutting back the number of links on the home page by a factor of 10 if you if you change a home page so that it goes from linking to 600 pages to linking to the less than 100 that you actually want to rank that will almost always have a massive difference a massive impact more so than external link building could ever dream of because you're not going to get that 10 times difference through external link building x unless it's a startup or something so yeah some some real old scenarios I want to talk about basically some things that SEO tools often flag that we're all familiar with talking about as as SEO issues or optimizations or whatever but often we don't think about why and we definitely don't think of them as being things that are part back it's quite so so deep into Google's history so a redirect is a link that the fictional idea of a page with one link on it is a redirect because a redirect is just a page that links to exactly one other page so in this scenario the page on the left could have linked directly to the page in the top right but because it didn't we've got this 0.85 squared here which is 0.7 225 the only thing you need to know about that is that it's a smaller number than 0.85 because we didn't link directly we went through this page here that redirected which doesn't feel like a link but is a link in this in this ecosystem we've just arbitrarily decided to dilute the page in the cycle and this is obviously particularly particularly important when we think about chain redirects which is another thing that's often flagged by SEO tools but when you look in an issue report in something like moz pro and it said and it gives you a list of redirects as if they're issues that can be confusing because a redirect is something we're also told is a good thing right like if we have a URL that's no longer in use it should redirect but what the reason that issue is being flagged is we shouldn't still be linking to the URL redirects we should be linking directly to the thing at the end of the chain and this is why it's because this arbitrary dilution that we're we're inserting into our own website which is basically just a dead weight loss if you imagine that in reality pages do tend to link back to each other you know this will be a big complex web and cycle that is and I think this is where the flow thing comes around because people can imagine a flow of buckets that drip round into each other but leak a little bit at every step and then you get less and less water and an SSM external source if you imagine these are looking background then inserting reader x is just you know dead weight loss we've drilled a hole in the bottom of a bucket so yeah better as direct link worse as a 302 although that's a controversial subject who knows that google sometimes claim that they treat 302s as 301s these days let's not get into that canonicals very similar a canonical from a page rank perspective a canonical is actually a much later addition to search engines but the economical is basically equivalent to a 301 redirect so if we have this badgers page which has two versions so you can access it by going to badgers question mark color equals brown or you can so I imagine I have a website that sells live badgers for some reason in different colors and then I might have these two different url variants for my my badger econ page filtered to brown and I decided that this one without any parameters without any parameters is the is the canonical version literally and figuratively speaking if the homepage links to it via this parameter page which then has a canonical tag pointing at the correct version then I've arbitrarily weakened the the correct version versus what I could have done which would be the direct link through interestingly if we do have this direct link through note that this page now has no strength at all there's it's now has no inbound links and also it probably wouldn't get flagged as an error in a tool because the tool wouldn't find it that you'll notice I put a tilde before the number zero we'll we'll come to that page rank sculpting and is another thing that I think is interesting because people still try to do it even though it's not worked for a really long time and this is so this is an imaginary scenario that is not imaginary at all it's really common most probably has this exact scenario where your homepage links to some pages you care about and also some pages you don't really care about certainly from an SEO perspective such as your privacy policy kind of sucks because in this extreme example here having a privacy policy is just randomly halved the strength of a page you care about no one wants that and so what people used to do was they would use a link level nofollow they use a link level nofollow which so the idea was and it worked at the time and by at the time I mean like 2002 or something um but people still try this on new websites today the idea was that by effectively the link level nofollow removed this link so it was as if your homepage only linked to one page great everyone's winner side note I talked about so no page actually has zero page rank a page with no links in the page rank model has the has the page rank one over the number the number of pages on the internet that's the seeding probability that at the start of before everything starts going and the cycles round and figures out what the stable equilibrium page rank is they assume that there's an equal chance you're on any page on the internet one divided by the number of pages on the internet is a very small number so we can think of it as zero this was changed and our little nofollow hack was changed again a very very long time ago and such that if you use a link level nofollow and by the way this is also true if you use a robots dot text to do this this link this second link will still be counted in when we when we go here and we have this divided by two to say we're we're halving you know there's an equal chance that you go to either of these pages this page still gets that reduction because it was one of two links but this page at the bottom now has no strength at all because it was only linked to a nofollow so this is kind of a if you do this now it's a worst of both worlds scenario and you might say oh I don't actually care whether my privacy policy has zero strength you know whatever but you do care because your privacy policy probably links through the top now to every other page on your website so you're still doing yourself a disservice at second side note I said link level nofollow meaning nofollow in the hml is an attribute of a link there is also page level nofollow which I struggled to think of a single good use case for that's basically a page level nofollow means we are going to treat every single link on this page as nofollow so we're just going to create a page rank dead end this is a strange thing to do so sometimes people use robots.txt which basically does the same thing like if I block this page of robots.txt that's the same in terms of the page rank consequences except there are other good reasons to do that like I might not want Google to ever see this or I might want to prevent a massive waste of Google's crawlers time so that they spend more time calling the rest of my site or something like this there are reasons to use robots.txt page level nofollow is you know we're we're going to create that dead end but also we're going to waste Google's time calling it anyway this some of the extreme scenarios I just talked about particularly the one with the privacy policy changed a lot in for the better for everyone in 2004 with something called reasonable surfer which you occasionally still hear people talking about now but mostly implicitly and it's probably actually an under discussed or under held in mind topic so these days and by these days I mean for the last 17 years if one of these links is was that massive call to action and another one of these links was in the photo like a privacy policy link often is then Google will apply some sense and say well the chance people click on this one is very we were trying to figure out probabilities here remember so we're just we'll split this this 0.9 and not that one still have to add up to one but we'll split them in a more reasonable fashion yeah they were doing that a long time ago they've probably got very very good at it by now no index is an interesting one because traditionally you would think that has nothing to do with page rank and so yeah no index tag just means this should never show up in search results this page at the bottom which is fine there are some valid reasons to to do that and maybe you're worried that it will show up for the wrong query that something else in your site is trying to show up for or maybe it contains sensitive information or something like this okay fine however when you put a no index tag on something Google eventually stops calling it and this only emerged with everyone sort of intuitively knew all the pieces of this puzzle but it only emerged that Google only acknowledged that this behavior is what happens a couple of years ago so Google eventually stops crawling it and when Google stops crawling on it it it stops passing page rank so no index follow which used to be a quite a good thing or we thought quite a good thing to do for a page like an HTML site map page or something like that like an HTML site map page clearly you don't want to show up in search results because it's kind of crap and a poor reflection on your site and not a good UX and this kind of thing but it is a good way to pass equity through to a bunch of deep pages right or so we thought and it turns out probably not you know it's it was equivalent to that worst case scenario no page level no follow in the long run that we talked about earlier and again this is this is probably why no index is flagged as an error in tools like mozpro although obviously often it's not well explained or understood my pet there and how links work is that at this stage they're no longer a popularity proxy because there's better ways of doing that but they are a brand proxy and you know a frequently cited brand you know a citation and link are often used synonymously in this industry right so that kind of makes sense however once you actually start ranking in the top five or ten my experience is that links become less and less relevant the more and more competitive a position you're in because google has increasingly better dates to figure out whether people want to click on you or not this is some data from 2009 and contrasting ranking correlations in positions six to ten versus positions one to five basically both brand and link become less relevant and in or the easily measured versions become less relevant and which again is kind of exploring that theory that the higher up you rank the more bespoke and user signal based it might become this is some older data where I basically looked at to what extent you can use domain authority to predict rankings which is this blue bar to what extent you could use branded search volume to predict rankings which is a screen bar and to what extent you could use a model containing them both to predict rankings which is not really any better than just using branded search volume this is obviously simplified and flawed data but this is some evidence towards the hypothesis that links are used as a brand proxy