The first study cited below seemed to indicate that engagement strategies did not affect the online retention rate. Further down in the article, another campus tried the intervention of informal advisors (like those in our GET REAL Center) or student peer mentors, and that did seem to have a positive effect. One thing is clear: retention rates do seem to be consistently lower in online courses, and time management skills are key to student success in them.

Preventing Online Dropouts: Does Anything Work? – Wired Campus – The Chronicle of Higher Education.