Google Analytics Accuracy – Or Lack Thereof

How to Use and Interpret Google Analytics Correctly

Google Analytics Accuracy vs. Webserver Log FilesGoogle Analytics is notoriously unreliable, and there are multiple issues that impact on its accuracy, including the software platform it’s operating from. That would not be a problem if the average website owner / user actually understood real purpose of Google Analytics.
Analytics is NOT designed to record website traffic statistics accurately. Google Analytics is far from accurate, especially when compared directly against server log files.  GA is instead designed and intended to monitor and analyse what people do when on the site. That’s why its called “Google Analytics” and not “Google Statistics”…
Variations between Google Analytics and web server log files can vary from 10% to as much as 75%… That variation depends on the site architecture, any conflicting JavaScript code and sundry other variables!

GA results are indicative rather than absolute, and are best used to identify trends, assess poor performing pages, monitor effectiveness of Adwords advertising campaigns and track visitor behaviour on the site. GA should never be seen as an accurate way to measure web site traffic – that’s NOT what its designed for. Despite that, there is endless discussion on this topic across the globe…

A client asked me this question recently;

Why are you adverse to Google Analytics?  Surely if one uses that consistently it is a constant so even if it is not 100% accurate the information it provides is relative.

My unsympathetic answer was;

Trying to use Google Analytics to assess web site traffic is like using a screwdriver to undo a nut… And yes, you can keep doing it over and over again. However, the RESULT is ALWAYS going to be suboptimal!”

How to use Google Analytics to Track Visitor Activities

Google Analytics is designed to monitor;

  • what people do when they are on your website
  • the pages they landed on
  • where they go internally
  • where they exit from.

It’s a behavioural tool… Its good at measuring conversion ratios – what percentage of people follow the traffic flow “funnel” you’ve visualised and end up doing whatever it is you’d like them to do. Regardless of whether that’s making a purchase, filling in a contact form or joining a mailing list, you’d like to know if things are getting worse or better…

You can edit a page and monitor the impact on conversions… you can alter your Unique Selling Proposition, or Call to Action, and measure the impact…

However, because GA is running as a tack-on chunk of JavaScript code at the bottom of your pages and passing information to your Google account, its prone to both interference and error… Other JavaScript elements on the site, site and web server software and coding may easily interfere with Google Analytics accuracy and performance…

Google Analytics Limitations

(Source: Wikipedia)

Many ad filtering programs and extensions (such as Firefox’s Adblock and NoScript) can block the GATC. This prevents some traffic and users from being tracked, and leads to holes in the collected data. Also, privacy networks like Tor will mask the user’s actual location and present inaccurate geographical data. Some users do not have Javascript-enabled/capable browsers or turn this feature off. However, these limitations are considered small – affecting only a small percentage of visits.

The largest potential impact on data accuracy comes from users deleting or blocking Google Analytics cookies. Without cookies being set, GA cannot collect data. Any individual web user can block or delete cookies resulting in the data loss of those visits for GA users. Website owners can encourage users not to disable cookies, for example by making visitors more comfortable using the site through posting a privacy policy.

Because GA uses a page tagging technique to collect visitor information via a combination of JavaScript and cookies, it has limitations with websites browsed from mobile phones. This is due to the fact that only the latest phones are currently able to run JavaScript or set cookies (Smart phones and PDAs).

These limitations affect all on-site web analytics tools that collect on-site visitor data using page tags. That is, the small piece of code (usually JavaScript) that acts as a beacon to collect visitor data.

Another limitation of GA for large websites is the use of sampling in the generation of many of its reports. To reduce the load on their servers and to provide users with a relatively quick response for their query, GA limits reports to 200,000 randomly sampled visits at the profile level for its calculations. While margins of error are indicated for the visits metric, margins of error are not provided for any other metrics in the GA reports. For small segments of data, the margin of error can be very large.

Other Ways That Dilute Accuracy of Google Analytics results

  • Many people also set their browser to clear cookies on exit
  • Other JavaScript applications may interfere with Google analytics results
  • Code may not be correctly implemented

How to Get Accurate Website Traffic Analysis

If you want to know the answers to the “how many” type of questions then you should look in the server log files using AwStats or Webalizer. These are installed on and accessible from, most hosting account…

Real traffic volumes are measured extremely accurately by the web server, and recorded in log files in (almost) all hosting accounts. To really see what’s happening, you need to look at the hosting account’s traffic analyser software. Usually either Webaliser, or AwStats (or both).

Of the two, AwStats is best because it excludes visits from all known search engine spiders and indexing agents, giving a much more accurate picture. Webaliser figures are often 30% – 50% higher because of that distortion.

Website Statistics Summary

You want to know more than either Google Analytics or server log files can tell you on their own;

  1. You can implement  Google Analytics on your website, to track where people go. That requires the insertion of a small block of JavaScript code in the footer. Visitor information is then channelled from your website to your Google account.
  2. You can look at your hosting account’s website traffic statistics, to assess total visitors, where they came from, how long they stay etc.

To really understand whats happening, you need to use BOTH mechanisms… and you need to understand the strengths and weaknesses of each.