Alexa

Alexa (or Alexa Internet) was a website that collected data on website visitors. Originally, the site only collected data based on the browsing patterns of users who had installed the company's software tool on their browsers. Later, Alexa claimed that it had expanded its data collection procedure to include additional sources, but the details were not made public.

Alexa's traffic rankings for websites that reach large percentages of Internet users, such as Wikipedia and Google may have been fairly accurate, at least for tracking trends. But the company also reported traffic ranks for their top 100,000 rated sites, often reaching so far into the tails of the distribution that the margins of error would overwhelm any actual potential ranking. Likely any ranking below about the top 1000 is dominated by error and worthless.

Beyond traffic rankings, Alexa embraced the voodoo of demographic tracking. Based on the few cookies it has access to, the operating system and browser used, Alexa claimed to be able to tell a site visitor's age, education level, number of children, gender, and whether the site was accessed from work, home or school. The way this demographic information was supposedly gleaned was not published, but the likelihood that even the most basic information (gender, age, location) was even remotely based on the true population of users is extremely small. The more specific demographic information can be completely disregarded.

The service shut down in May 2022.