Forum Moderators: DixonJones
This is probably the most common newbie question from people who have used the two different sources of data, server logs and javascript tags.
There are some detailed replies elsewhere in this forum going back several years. Part of the short version is that the javascript tagging method, for various reasons, contains virtually no hits by spiders or bots, as well as no downloads of untaggable files like pdfs.
This can be a huge difference, possibly as big as 50%.
On the other hand, the javscript method picks up backbutton clicks (i.e. cached views of pages) and server logs usually do not. The difference caused by this factor is a lot smaller than the spider/bot different, for most sites.