I assume that most web analytics tools identify the IE version by looking for MSIE X.Y in the browser string. However, this is no longer valid for IE8. This is because the IE8 user agent string will include MSIE 7.0 when in compatibility mode. The difference between the “real” IE7, and IE8 in compatibility mode is the word Trident, which is included in both variants of IE8:

Example of a regular IE8 user agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; SLCC1; Media Center PC 5.0; .NET CLR 3.5.21022)

Example of IE8 in compatibility mode: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; Trident/4.0; SLCC1; Media Center PC 5.0; .NET CLR 3.5.21022)

Literally thousands of web sites are not compatible with IE8. A list of more than 3,000 incompatible sites is maintained by Microsoft. This list can be downloaded by IE8 users so that the browser can automatically switch itself into compatibility view when a site is encountered that has previously been identified by IE8 users as incompatible. Many more sites are not compatible, but are not on the list because they have lower traffic levels.

Because a visitor can have multiple user agents in one visit, this raises a number of questions:

• Does your analytics tool keep the user agent string from each individual page view, or do they associate one browser with the entire visit?
• If browser is associated with the entire visit, which browser is recorded? If they keep the string on the entry page, then IE8 is likely represented correctly in your data, but you won’t know if users are resorting to compatibility mode in order to view your site. If your analytics tool keeps the last browser string encountered in the visit, then your numbers are likely biased toward IE7 unless your tool is properly grouping this traffic as IE8.
• If browser is associated with page views instead of the visit, then adding up visits in your browser report would give you more than the total visits for your site. In other words, browser visits would not be “summable” the way they are when one can assume that each visit has only one browser. This is not the end of the world, just something to be aware of because it’s not intuitive.
• Does your analytics tool properly group the browsers with both MSIE 7.0 and Trident as IE8? If not, do they expose the entire string so you can do the calculations yourself to see if your site has IE8 issues?
• If you are doing logfile analysis without cookies, sessionization is probably based on IP + User Agent. For sites where I’ve transitioned from logfiles to tags in the same tool, my experience has been that IP/User Agent sessionization tends to over-count visits: this issue will increase that inflation even more. Bear in mind that many tag-based tools resort to IP/UA when cookies are blocked, so there could be a small inflation effect regardless of the type of data-collection you use.

I examined a few of my sites and found the percentage of visits with IE8 to be roughly between 5% and 15%, depending on the site. My B2B sites tend to have lower IE8 penetration, while sites that attract high-tech users will tend to show a higher percentage of the latest browsers.

If your web analytics tool exposes the entire browser string (Google Analytics does not), I recommend you search through your user agent strings looking for Trident, and see for yourself if this is an issue for the sites you analyze. One metric I’m looking at is the percentage of my Trident browser visits that also contain MSIE 7, assuming that sites that are not compatible with IE8 will show a higher percentage of users resorting to compatibility mode. For a site with known IE8 issues I calculated 25% , while another site I randomly chose calculated to 12%. I haven’t examined enough sites yet to know if that means the second site also has IE8 issues, or if it just means it’s “normal” for a certain percentage of IE8 users to surf in compatibility mode. Clearly I have more work to do.

Update: Last night I received an email from a colleague who had read this post, asking why should they care? It’s a fair question so I thought I’d answer it publicly.

First, if you’re asking then you probably aren’t in a situation where you need to care. That’s OK: the lowly browser report isn’t the most important report in your web analytics tool, not by a long shot.

But I can think of a couple of situations where it’s important:

1. When deciding whether or not to fund development changes to enable compatibility with certain browsers, “fewer than 5% of our visits use that browser” is a lot different than “nearly 10% of our visits use that browser”.  The numbers you use for those decisions should be as accurate as practical.

2. Your customer service department may receive emails or phone calls from visitors complaining that they are unable to perform certain tasks on your site (like complete a transaction). When they receive multiple complaints that sound similar but are unable to reproduce the problem in house they may ask you, the analytics ninja, for help defining the scope of the problem. These intermittent issues are difficult to troubleshoot because they’re often environment-related. One starting point is to examine the user experience through that transaction — transaction page views per visit is sometimes sufficient, or you may want to look at a funnel chart for the process — and segment it by different browser versions. If the issue is due to a browser incompatibility, you can sometimes pinpoint it quickly with this type of analysis.