Research on Left Navigation

Kingsbury and Andre (2004) conducted a study to determine which Web-based three-level navigational selection pattern elicited the best human performance and highest user preference. They surveyed 69 Web sites and found that most of them favored a three-level navigational selection structure that was either:

* The initial selection was made from the top followed by a selection from the left navigation panel and subsequent selections from the left navigation panel (TLL).
* Left selection followed by subsequent left navigation selections (LLL).


more info is available in following link:
http://www.usability.gov/pubs/040106news.html