alexa

Alexa Internet is a California-based subsidiary company of Amazon.com, that is best known for operating a website (www.alexa.com) that provides information on the web traffic to other websites. Its premises are in Building 37 of the Presidio of San Francisco.

Founded in 1996 by Brewster Kahle and Bruce Gilliat and backed by Jacqui Safra's Etoile Investments as a commercial offshoot of the Internet Archive, Alexa Internet created related links derived from user behavior (a form of collaborative filtering) for users of the Internet Explorer and Netscape Navigator web browsers. Engineers at Alexa created the Internet Archive's Wayback Machine. Alexa also supplies the Internet Archive with web crawls. It should be noted that Alexa's official toolbar only works with a Windows/Internet Explorer 5.0+ [1], though there is a plugin for Mozilla Firefox called search status that accesses both Google and Alexa feeds.

In 1999, Alexa was acquired by Amazon.com for about $250 million in Amazon stock.

Alexa collects information on Web usage through the Windows-only / Internet Explorer-only application, the Alexa Toolbar. This allows them to provide statistics on web site traffic, as well as related link information. The Alexa Toolbar has a bad reputation with anti-spyware programs, as it collects information on search habits.

The "site info" link on the Alexa site lists related links for websites and also records how much web traffic they receive. Alexa began a partnership with Google in spring 2002, and with the Open Directory Project in January 2003. Windows Live Search replaced Google as a provider of search results in May 2006. In September 2006 they began using their Search Platform to serve results. Today, Alexa is primarily a search engine, an Open Directory-based web directory, and a supplier of site information.

Alexa also provides "site info" for the A9.com search engine and for Alexadex.com.

In December 2005, Alexa opened its extensive search index and web-crawling facilities to third party programs through a comprehensive set of web services and APIs. These could be used for instance to construct vertical search engines that could run on Alexa's own servers or elsewhere.

In September 2006, Alexa began using its own search platform to serve search results on its main website.

Alexa rank information

Alexa ranks sites based on visits from users of the Alexa Toolbar which is only available for Internet Explorer and must be manually installed. There is some controversy over how representative Alexa's user base is of typical internet behavior. If Alexa's user base were a fair statistical sample of the internet user population (e.g. a random sample of sufficient size), Alexa's ranking would be quite accurate (see Sampling). In reality, the sample is not random and has many sources of bias. Alexa itself notes several (here and here)

Preferential bias towards Alexa-listed sites		Sites that are featured on alexa.com are overrepresented.
Omission of some browsers		Users running any browser except Internet Explorer and Mozilla Firefox are not represented. Thus users of Opera, Safari, mobile phone (WAP) browsers are all ignored. Nevertheless, this is still the vast majority of the browser market.
Exclusion or strong negative bias for users of non-Windows computers		There is an unknown but strong bias with respect to operating systems, since most Internet Explorer users are running versions of Microsoft Windows. This both influences the sites they visit and misreports sites visited by users of other operating systems. Other platforms such as Linux and OS X do not use Internet Explorer and are ignored.
Omission of sites and visits using secure https, RSS or other non-HTML feeds		Visits to secure pages (https:) and newsfeeds (RSS) are not taken into account. Some sites serve a high proportion of these pages. RSS services and users are also under-represented from sites that serve both html and RSS because RSS feed-reading and aggregation software can't use the Alexa toolbar and so are not counted.
Omission of non-toolbar users		Users who do not install toolbars are not represented. Notably, this includes most corporate users, many work users, and most users of public computers such as libraries.
Omission of users with spyware/adware blockers		Users running spyware and adware prevention programs are under-represented or ignored.
Strong bias against experienced Internet users		Experienced users fall disproportionately into many of these categories. They are more often users of non-Microsoft browsers and operating systems, and they possess the technical knowledge to be avoidant of adware and spyware.

As a result of these biases, sites with a large share of visitors (especially experienced visitors or people browsing from work) who use non-IE browsers or are running on GNU/Linux or Mac OS, will appear quite low in Alexa rankings. Sites serving pages over secure connection or having large share of users concerned about privacy will also rank low.

In addition, the sample used for estimation is small comparatively to the population of all web users. Sites with low traffic can be completely missed in this small sample. Another concern connected here is that Alexa ratings are easily manipulated. Webmasters can significantly improve the Alexa ranking of less popular sites by making them the default page and by having Alexa toolbar installed ^[1].

Alexa provides an important, useful, and, for most websites, also independent source of information about website traffic. It reports some share of the traffic created by Alexa toolbar users. One can infer that the total traffic of the website is no less than what Alexa reports (but may be much more, since Alexa fails to account a large number of visitors). Unfortunately, Alexa's rankings are often misinterpreted as an exact or approximate measure of popularity of web sites.

See also

• List of internet search engines
• List of web directories
• Alexa Toolbar
• Spyware
• List of websites by number of visitors

External links

• Alexa Internet - official site
  • About the Alexa Traffic Rankings
  • Alexa's web search API platform
• The Internet Archive - official site
• Alexaholic
• Alexa Radar
• GoLexa
• Alexa Traffic Rank Firefox Search Plugin
• Debunking Alexa's Internet Ranking