I know this has been widely documented and commented on before, but I can't get to the bottom of the significant differences between data being reported in google analytics vs. that in adwords.
On one of our sites, (we only promote via adwords) we have analytics set up and are seeing the followng:

1) Adwords is reporting roughly double the clicks vs. number of visits Analytics is reporting

2) This varies up and down by day but it is generally double.

Even with google explanations like the below text ("clicks vs. Vistis") - I still can't believe the discrepancy is that much. We are talking thousands of clicks per day differences across the campaign just for this one site and are seeing similar patterns (although I admit this is the worst) on other sites & campaigns. Does anyone have any further thoughts / observations/advice?

Thanks
golles

"Clicks vs. Visits

There is an important distinction between clicks (such as in your All CPC Analysis or AdWords Analysis reports) and visits (in your CPC vs. Organic Conversion report). The clicks column in your reports indicates how many times your advertisements were clicked by visitors, while visits indicates the number of unique sessions initiated by your visitors. There are several reasons why these two numbers may not match:

* A visitor may click your ad multiple times. When one person clicks on one advertisement multiple times in the same session, AdWords will record multiple clicks while Analytics recognizes the separate pageviews as one visit. This is a common behavior among visitors engaging in comparison shopping.

* A user may click on an ad, and then later, during a different session, return directly to the site through a bookmark. The referral information from the original visit will be retained in this case, so the one click will result in multiple visits.

* A visitor may click on your advertisement, but prevent the page from fully loading by navigating to another page or by pressing their browser's Stop button. In this case, the Analytics tracking code is unable to execute and send tracking data to the Google servers. However, AdWords will still register a click.

* To ensure more accurate billing, Google AdWords automatically filters invalid clicks from your reports. However, Analytics reports these clicks as visits to your website in order to show the complete set of traffic data."