I typically utilize Alexa and Compete or others as a good way to compare sites of a similar demographic. Having access to google analytics for two different sit

I typically utilize Alexa and Compete or others as a good way to compare sites of a similar demographic. Having access to google analytics for two different sites; one being my blog and the other site is the company I work at. I know that my blog gets about half the traffic of my companies site but the corporate site is ranked 370,673 and my blog is ranked 395,487. I would think there would be more of a difference in the two sites ranking. But if I compare several of our companies competitors sites the numbers seem to line up. The numbers also make sense as trend data for a single site. I know from monitoring my blog when there is a spike in traffic; Compete and Alexa show a spike in their rankings. Because Alexa captures their information through a browser plugin you want to make sure that the set of people that visit each site are equally likely to have the plugin installed. If people that read hacker news are half as likely to install the Alexa Plugin then people that read the new york times then there would be variability in comparing those two site.