WP Super Cache and WordPress.com Stats are two very useful WordPress plugins. WP Super Cache provides static and dynamic cache functionality to reduce the load on your blog’s server, allowing larger amounts of traffic to visit without slowing the site down. WordPress.com Stats tracks visitors and gives valuable information on how users utilize your blog. If you plan to use both of them together, you should be careful though.
What happens when you have WP Super Cache enabled? If you visit a page that is not cached, a cache will be generated. If you are logged in at that time, the cached page will not have the stat updating code. This page will then be served to future users, whether they are logged in or not, resulting in lost statistics. This is a problem for all statistics tracking that relies on checking if users are guests or not.
The solution is to check the option in WP Super Cache called “Don’t cache pages for logged in users.” This will cause cached pages to always be for guests only, and thus contain the stat updating code. Be sure to clear the existing cache after enabling this option to make sure the wrongly cached pages are gone.