Ask YC: How do sites like Compete, Alexa collect traffic estimates?
I've always been curious.
Other sites, like Comscore, use various methods like router-level analysis & client-side monitoring software (like Nielson w/ TVs).
In the end, no method is 100% accurate and the best analysis comes from looking at various sources & taking it all with a grain of salt.
it seems like collecting data like search engine queries, number of inbound links to the site might also be used. no?
At the end of the day, everyone who owns a blog or a website (myself included) has been able to experience first hand how flawed the data from such companies are by simply comparing them with their own google analytics data :-)