eHealth—the organisation and delivery of health services and information using information technology (IT) systems—is playing an increasingly important role in shaping health care systems. This week PLoS Medicine publishes the third in a series of articles evaluating eHealth. Richard Lilford and colleagues consider the evaluation of health IT systems as they are employed following pre-implementation testing.

The authors point out the necessity for evaluation of eHealth computer systems and the difficulties such evaluation will encounter. "There is a consensus about the evaluation of clinical treatments, such as drugs, in which randomized control trials are state of the art," they say. "No such consensus exists yet for the evaluation of highly complex service interventions such as computer systems." The authors conclude that "multiple methods research" is necessary for eHealth systems evaluation: "Research commissioners and research teams need to recognize the importance of undertaking combined quantitative and qualitative work when evaluating IT systems."