In their 2011 publication, "Instructor's Discussion Forum Effort: Is It Worth It?" in the Journal of Online Learning and Teaching, Michelle Cranney, Lisa Wallace, Jeffrey L. Alexander, and Laura Alfano report:

The popularity of virtual education resulted in institutions seeking best practices as a guide to providing a quality education to online students. The purpose of this retrospective, correlation study was to examine online instructors' discussion forum participation, including time spent on a weekly basis overall in the course and number of posts to discussion forums, to determine if there was a positive effect on students' overall discussion grades. The study included 10 purposively selected courses. Statistics were used to define the sample population. Statistical calculations indicated no correlation between the numbers of posts to the discussion forums to student grades, but a positive correlation exists between the amount of time spent by the instructor in class to higher discussion grades earned by students. The findings of this study will help to identify criteria that educational institutions can use to develop best practices for online instructors.

To read the full article, see: http://jolt.merlot.org/vol7no3/cranney_0911.htm