How do we know if e-learning is effective?

Amidst all the enthusiasm and claims about technology transforming the way we teach and learn, is there also a body of evidence to support the premise that e-learning helps people learn: is it effective? A team at the University of Sussex has conducted a modified systematic review of the literature in order to investigate these questions: What works in eLearning? How do we know it works? What factors influence how well it works?