IDEAL framework for surgical innovation 2: observational studies in the exploration and assessment stages.

The IDEAL framework describes the stages of evaluation for surgical innovations. This paper considers the role of observational studies in the exploration and assessment stages. At the exploration stage, the surgical intervention is usually more widely used, and observational studies should collect prospective data from multiple surgeons, deal with factors such as case mix and learning, and prepare for a definitive evaluation at the next stage of assessment. Although a randomised controlled trial is preferable, a high quality observational study would be acceptable if a randomised trial is not feasible or, on rare occasions, deemed unnecessary