'Real-world' clinical trials in diabetes care: meaningful or meaningless?

So-called 'real-world' studies seem increasingly popular in diabetes care, as are the economic evaluations in secondary literature based upon them. The term is usually used for pharmacoepidemiological uncontrolled observational studies of different designs. Interpretation of the study findings is, however, badly undermined by the very reasons that the randomised controlled blinded study was invented - namely, non-medication study effects and biases in investigator selection and behaviour. In diabetes studies, glucose control seems particularly susceptible to such effects, perhaps through changes in patient motivation and education. Further, insulin studies are heavily influenced by baseline factors such as the site of starting insulin, the health circumstances of the patient at the time and the clinician involved. It is rare to see these issues adequately addressed or attempts made to understand their influence. In this article an attempt is made to discuss some of the issues further.