Alexa uses it’s toolbar to rank websites.
This can be a decent judge, but of course it misses alot of traffic. I mean alot.
It grossly underestimating certain markets of the Internet. Many people have not heard of Alexa not to talk of downloading their toolbar.
Compete solves this by using multiple sources like it’s toolbar, ISP data and opt-in panels.
Yes some ISPs are sharing your browsing data. Not all but some. I believe more will enter this market, considering they can generate more revenue.
Show Compete your Traffic
If your ISP is not sharing your data, download the Compete Toolbar. It’s available for IE and Firefox.
Compete Info: Unique visitors are counted once a month. Most people’s rankings are about 4-5 times their Alexa rank.
More Tools to Gauge Popularity
In addition to PageRank, Alexa, Compete and Technorati Ranking. Look out for Text-Link-Ads and ReviewMe to include their site rankings options. Keep in mind all of these tools provide statistics. Which are not the most accurate figures. Google analytics is more accurate because of the javascript you have to add to your website, but you don’t have access to your competitors figures so it’s not good for comparison.