Why are Awstats, Webalizer, and Google Analytics results so different?

Question

I realize that comparing Awstats and Webalizer to Google Analytics is like comparing apples to oranges, but each of them track at least basic statistics about visitors and pages.

So why are there often very significant differences in their data?

For example, comparing Analytics with Awstats using some numbers from a small site over the past week:

Awstats

• 78 unique visitors
• 205 visits (2.62 visits/visitor)
• 1,072 pages (5.22 pages/visit)

Google Analytics

• 115 unique visitors
• 240 visits (2.08 visits/visitor)
• 1,275 pages (5.31 pages/visit)

They're similar on the number of visits, but page views and uniques are quite different. I'm familiar with discrepancies of a much higher magnitude on some larger sites, showing that this trend scales proportionally upward.

What is the reason behind the different numbers, even when the data is quite trivial like unique visitors and page loads?

Answer 1

What is the reason behind the different numbers, even when the data is quite trivial like unique visitors and page loads?

Google Analytics requires a Javascript callback to Google's domain and will not record traffic from users with Javascript disabled or the majority of bots.

AWStats is literally reading your webserver's logs and will record (in one fashion or another) the bots it is programmed to recognize, visitors, and (where your discrepancy likely lies) it will also report bots it does not recognize as visitors.

See What are some advantages of using Analytics like Urchin? and What are the pros & cons of web server log analysis over web based analytics like google analytics? for further explanation.