measures and metrics for website qualityQuantifying how good a website is very difficult. What are the signs of a great website? Plenty of visitors, lots of links from other large and excellent websites, Facebook fans, mentions on Twitter, good clean HTML and attractive design. Rolling all that information up into a single, easy to understand metric is very tricky. Then there is the question of actually extracting all that input information in the first place. Some of those factors can’t really be quantified, especially without human intervention.

PageRank looks primarily at your link profile

There are two popular approaches to measuring website quality. The most common looks at the link profile on the assumption that good sites get more links. PageRank (PR) is the best known of these metrics, and it takes into account both the number of inbound links and the quality of linking sites. It’s usually expressed as a digit ranging from zero to ten, the higher the better. It’s been around for a while and it’s nice and simple.

A lot of people use PageRank to attract linking partners and sell advertising space, but there is a problem. Published PageRanks are only updated every few months, so a new site that has worked hard for three months and now has plenty of inbound links may still have zero PR. Many pro bloggers and SEO folks have moved away from PR for that reason. The replacement metric of choice is usually mozRank, which uses similar concepts but leaves behind the delay problem that annoys so many low PR webmasters. It ranges from 0 to 10 and is a little more precise than PR, because values are reported to two decimal places.

Replacing PageRank with MozRank

There are a few variations on mozRank, but perhaps the most powerful is the concept of mozRank Passed. This metric aims to quantify the amount of power a link from a particular page conveys. It takes into account the number of outbound links, the page’s own mozRank and several other factors. It’s not in popular use yet, so it’ll be very interesting to see whether the SEO community thinks this measure is valuable over the long term.

Alexa takes a look at your traffic

The second site evaluation strategy is to use the number of visitors. That’s all very well for webmasters who have access to their own visitor data, but when you want to check out the competition you won’t have access to their analytics accounts. So, how to estimate visitor activity? Alexa Rank is the most widely used metric of this kind, and they use browsing data collected from every user with an Alexa Toolbar installed. Their rank is based on a relatively small subset of internet users- the exact number of Alexa Tool users isn’t public knowledge- but downloads number in the tens of millions.

Because it’s based on small statistical sample, Alexa Rank is only really useful for big sites. It is a true rank with values ranging from the millions to number one, the lower the better. Google firmly occupies the top spot, followed by Facebook and YouTube. An active PR5 commercial website might have an Alexa Rank in the hundreds of thousands, and a value of a million is reasonable for a medium-sized PR3 blog.

No Single Metric Gives a Proper Pictures of Website Quality

While it’s quick and convenient to quote PR, mozRank, and Alexa Rank (and many people pick just one), no single measure gives a full picture of website quality. As a mathematician I hate to say it, but the best tool for evaluating a site is still the human eye. Does the design look sharp? Is the navigation easy and intuitive? Is it actively updated? Most importantly, is it useful, funny, or interesting?

Numerical metrics are great, but they still need to be combined with the evaluation of a human being to be really informative. When you’re looking for a linking partner or evaluating a business opportunity online, always check the PR and the other ranks, but use your own judgement too. Sites that are obviously putting a lot of effort into content may start out ranking poorly but they’ll soon start to rise- just because a site has zero PR and low mozRank doesn’t mean it won’t make a good investment.

Image: Paul /