How accurate is Google Analytics?

That’s the question that I was asked recently by one of the co-workers.   It is simple and not so simple at the same time.  It really depends on what you are looking for, what is the acceptable accuracy, and what is that you are comparing Google Analytics with.

For example, if you compare the numbers from your Google Analytics reports to the summaries of the web server logs, you’ll probably find that Google Analytics reports lower numbers.  Almost like not everything is recorded.  Which is true because Google Analytics is using JavaScript to track your visitors.  Server logs record all hits to your web server, but the information in logs is very limited – it won’t be enough for anything but very basic tracking.

How much will numbers differ?  Here is what Google Analytics blog has to say:

Google Analytics uses JavaScript tags to collect data. This industry-standard method yields reliable trends and a high degree of precision, but it’s not perfect. Most of the time, if you are noticing data discrepancies greater than 10%, it’s due to an installation issue. Common problems include JavaScript errors, redirects, untagged pages and slow client-side load times.

Having used Google Analytics on a number of sites over a number of years, I’d say that that is just about right.

4 thoughts on “How accurate is Google Analytics?”

  1. You could also try my script YMMV Real Webstats to check the accuracy of your Google Analytics. It compares the Google Analytics number and also tells you how many page-views are blocked by Adblock, noscript or other methods.

  2. According to one of my clients WMT's we have an average page load time of 1.5 seconds, so we are ruling out page loading issues. We have analysed all of our log files and compared them to our Analytics results and there is no regular pattern of javascript issues, untags and we have no redirects. Having said this we have shown the following discrepencies between our log file analysis and Analytics for the month so far:

    Log Files: Google Visits = 2674 | Yahoo Visits = 233 |
    Analytics: Google Web Visits = 1877 + Google Referals = 217 == 2094 | Yahoo Visits = 204

    I have not listed the total visitor number and page view differences because these immense differences ( Approx. 81% missing from Analytics) could be result of bots etc. But still quite a difference which I'm at a loss to find the reason for.

    Hope this helps your viewers ;-)

  3. They are using Urchin which was installed quite a while back. To be honest they only use their log file analysis now, for analyzing visitor path transits etc, and we leave the Google Analytics on to keep up relations with Google ;-) Don't know if this has any benefit, but all is appreciated eh?

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