Alexa Internet, Inc. is a California-based subsidiary company of Amazon.com that is best known for operating a website that provides information on web traffic to other websites.
Alexa Internet was founded in 1996 by Brewster Kahle and Bruce Gilliat.The company offered a toolbar that gave Internet users guidance on where to go next, based on the traffic patterns of its user community. Alexa also offered context for each site visited: to whom it was registered, how many pages it had, how many other sites pointed to it, and how frequently it was updated.Engineers at Alexa, in cooperation with the Internet Archive, created the Internet Archive's Wayback Machine.Alexa also supplies the Internet Archive with web crawls.
In 1999, Alexa was acquired by Amazon.com for about $250 million in Amazon stock.
A listing of all sites on the Web, sorted by traffic...
Alexa computes traffic rankings by analyzing the Web usage of millions of Alexa Toolbar users and data obtained from other, diverse traffic data sources. The information is sorted, sifted, anonymized, counted, and computed, until, finally, they get the traffic rankings shown in the Alexa service. The process is relatively complex, but if you have a need to know, please read on.
What is Traffic Rank?
The traffic rank is based on three months of aggregated historical traffic data from millions of Alexa Toolbar users and data obtained from other, diverse traffic data sources, and is a combined measure of page views and users (reach). As a first step, Alexa computes the reach and number of page views for all sites on the Web on a daily basis. The main Alexa traffic rank is based on a value derived from these two quantities averaged over time (so that the rank of a site reflects both the number of users who visit that site as well as the number of pages on the site viewed by those users). The three-month change is determined by comparing the site's current rank with its rank from three months ago. For example, on July 1, the three-month change would show the difference between the rank based on traffic during the first quarter of the year and the rank based on traffic during the second quarter.
What are sites and Web hosts?
Traffic is computed for sites, which are typically defined at the domain level. For example, the Web hosts www.msn.com, carpoint.msn.com and slate.msn.com are all treated as part of the same site, because they all reside on the same domain, msn.com. An exception is blogs or personal home pages, which are treated separately if they can be automatically identified as such from the URLs in question. Also, sites which are found to be serving the same content (mirrors) are generally counted together as the same site.
What is Reach?
Reach measures the number of users. Reach is typically expressed as the percentage of all Internet users who visit a given site. So, for example, if a site like yahoo.com has a reach of 28%, this means that of all global Internet users measured by Alexa, 28% of them visit yahoo.com. Alexa's one-week and three-month average reach are measures of daily reach, averaged over the specified time period. The three-month change is determined by comparing a site's current reach with its values from three months ago.
How Are Traffic Trend Graphs Calculated?
The Trend graph shows you a three-day moving average of the site's daily traffic rank, charted over time. The daily traffic rank reflects the traffic to the site based on data for a single day. In contrast, the main traffic rank shown in the Alexa Toolbar and elsewhere in the service is calculated from three months of aggregate traffic data.
Daily traffic rankings will sometimes benefit sites with sporadically high traffic, while the three-month traffic ranking benefits sites with consistent traffic over time. Since we feel that consistent traffic is a better indication of a site's value, we've chosen to use the three-month traffic rank to represent the site's overall popularity. We use the daily traffic rank in the Trend graphs because it allows you to see short-term fluctuations in traffic much more clearly.
It is possible for a site's three-month traffic rank to be higher than any single daily rank shown in the Trend graph. On any given day there may be many sites that temporarily shoot up in the rankings. But if a site has consistent traffic performance, it may end up with the best ranking when the traffic data are aggregated into the three-month average. A good analogy is a four-day golf tournament: if a different player comes in first at each match, but you come in second at all four matches, you can end up winning the tournament.
How are Movers & Shakers Calculated?
The movers and shakers list is based on changes in average reach (numbers of users). For each site on the net, we compute the average weekly reach and compare it with the average reach during previous weeks. The more significant the change, the higher the site will be on the list. The percent change shown on the Movers & Shakers list is based on the change in reach. It is important to note that the traffic rankings shown on the Movers & Shakers page are weekly traffic rankings; they are not the same as the three-month average traffic rankings shown in the other Alexa services and are not the same as the reach numbers used to generate the list.
(Courtesy : www.alexa.com)
