Usage share
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Usage share, in web browser statistics, is the percentage of visitors to a group of web sites that use a particular browser. For example, when it is said that Internet Explorer has a 85% usage share, that means that Internet Explorer is used by 85% of visitors that visit a given set of sites. Typically, the user agent string is used to identify which browser a visitor is using.
Overestimation and underestimation
Note that measuring browser usage in terms of the number of requests (page hits) made by each user agent can be misleading. Not all requests are generated by a user, as a user agent can make requests at regular time intervals without user input. In this case, the usage of that user agent would then be overestimated. Some examples:
- A web browser that refreshes the webpage at a regular time interval.
- A feed reader that requests the RSS/Atom feed at a regular time interval.
- Extra files like CSS hacks and JavaScript hacks are often sent to Internet Explorer as it contains a number of bugs and does not support W3C standards fully.
It is also possible to underestimate the usage share, for example:
- A graphical browser typically results in more requests than a text browser, as it downloads referred by the HTML document, e.g. image, CSS, and JavaScript.
- A computer with more memory will likely to cache more webpages in the memory, resulting in less requests.
These problems could be avoided by using measures in terms of unique visitors to web sites rather than page hits. This can be achieved by using IP address and cookies. However, many web statistics software that only gather data from the web server logs do not provide this kind of measurement.