Alexa's traffic rankings are based on the usage patterns of Alexa Toolbar users over a rolling 3 month period. A site's ranking is based on a combined measure of reach & pageviews. Reach is determined by the number of unique Alexa users who visit a site on a given day. Pageviews are the total number of Alexa user URL requests for a site. The site with the highest combination of users and pageviews is ranked #1.
But is this the correct way to judge or rank a website.
Apart from the biased that it is based on the sample of Alexa tool bar users, it is browser specific and it can be easily manipulated, the formula itself is debatable.
We started off by quoting the number of “Hits” for determining traffic of a website. But eventually, we moved away from the term "hit" because everyone realized it was pretty meaningless. A hit was often counted not just for a page load, but for every element included on the page, as well. So if a site was less graphical and had equal usage would register half the hits.
And then came Reach and Pageviews.
As such, it would not be fair to compare two websites that belong to different categories. But measuring reach (number of unique visitors) is important because mainstream advertisers want to reach a lot of people but not just the same people over and over. It also gives an idea of popularity and growth of a website.
Pageviews became the primary metric not because they were more meaningful but because they helped in closing Ads deals since Ads were sold primarily on a CPM basis and its counts are as susceptible as hit counts to site design decisions that have nothing to do with actual usage.
Someone has brilliantly analyzed that the part of the reason MySpace drives such an amazing number of pageviews is because their site design is so terrible.
As the way we interact with the web is changing, and technology makes it easier for users to have access to multimedia content on a single web page, are page views still relevant? AJAX, RSS, Feeds, Widgets. Streaming etc. are making things worse.
So what's a better way for comparison? Good question.
As I have mentioned earlier also, it is not fair to compare two websites that belong to different categories. The measurement of success also varies from website to website. So it could be registered users, files uploaded/downloaded, posts, hits, searches, revenue, and it may even be pageviews. But internal metrics aren't enough, since we want to compare ourselves to other players in the market. So we also need some apples-to-apples comparison.
If I had to pick one, in addition to unique visitors (reach), I'd say time spent would be much more useful than pageviews.
Time spent interacting with a site is a much better basis on which to compare sites' relative ability to capture attention/value than pageviews is. Especially when it comes to media like audio or video, an increasing percentage of the web consumption, time obviously means a great deal more than a pageview.
However, time is a bit harder to measure.
HTTP doesn't actually have a concept of time spent. So if you read this whole post and then click off to another site, my web server won't know whether you were here for five minutes or five seconds. I don’t even know whether you have been reading this post for last 10 mins or you are having a coffee with this page open in your browser.
Finally, there's a big argument against time as a measure:
People don't spend much time on Google search, because it gives them what they want so fast, and they go away (which is obviously good for them and for users). But the average time spent per visit will be very low.
And just as pageviews can be gamed, you can slow your users down unnecessarily (or accidentally because your servers are too slow) and increase time spent.
In short, there's no easy solution but there's a BIG opportunity (though very tough job) for someone to come up with a meaningful metric that weighs a bunch of factors.
Can you suggest any?