Huge difference in visits/hits between IIS logs and google analytics

Question

I use google analytics to monitor visitors access, and I am very happy with it, easy to use blabla, you name it :)

Few days ago I copied IIS logs from website and used free/evaluation commercial log parsers on the market to find out what RAW IIS logs tells me about the visitors. I was shocked that IIS tells me that I have 3x more visits/hits daily than in google analytics. Spiders are not included in IIS logs (filtered them via parse app).

What I assume is one amount of the hits have javascript disabled and there can be a small difference around 20% (I have that stats from another site).

What I don't understand is 3x difference between raw logs and GA. On the site we run product oriented site for the application that is used on windows servers, and windows servers by default have JS disabled, so I assume some of the users might be in that difference as well, just I don't understand 3x difference between numbers.

Any good explanation?

Answer 1

There are lots of bots (computer programs) that visit webpages. However, they pretend to be real users by using the user agent of a popular browser, such as IE or firefox or chrome; instead of using their own specialized user agent so the server knows they aren't real people. As a result, the IIS logs count them as real users. Google Analytics doesn't, because it is javascript based and the bots don't execute javascript.

Source: http://www.webmasterworld.com/analytics/3699288-2-30.htm

Answer 2

One thing you could try is analyzing your log files to look for users that are using Google Analytics. This should roughly match up with what GA is reporting then you can look at the rest closer to see what it is.

GA uses first party cookies so it should be possible to configure your server to log them then you can find GA users by selecting requests with the __utma cookie present. You could also parse __utma to identify unique visitors.