A few months ago I wrote in a blog post that incremental statistics cannot be combined with a small value for estimate_percent. Because this problem is still an issue for one of my customers (who runs a quite big Data Warehouse) I was looking for some additional information about this subject and found an excellent overview in the blog of Randolf Geist: Incremental Partition Statistics Review. It contains some interesting background information about incremental statistics and its limitations. If you plan to use incremental statistics in your Oracle 11g database, you should read this review summary first.